| Message ID | 20240701140017.49223-1-east.moutain.yang@gmail.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [v7] virtio-net: Fix network stall at the host side waiting for kick | expand |
On Mon, Jul 01, 2024 at 10:00:17PM +0800, Wencheng Yang wrote: > From: thomas <east.moutain.yang@gmail.com> > > Patch 06b12970174 ("virtio-net: fix network stall under load") > added double-check to test whether the available buffer size > can satisfy the request or not, in case the guest has added > some buffers to the avail ring simultaneously after the first > check. It will be lucky if the available buffer size becomes > okay after the double-check, then the host can send the packet > to the guest. If the buffer size still can't satisfy the request, > even if the guest has added some buffers, viritio-net would > stall at the host side forever. > > The patch checks whether the guest has added some buffers > after last check of avail idx when the available buffers are > not sufficient, if so then recheck the available buffers > in the loop. > > The patch also reverts patch "06b12970174". > > The case below can reproduce the stall. > > Guest 0 > +--------+ > | iperf | > ---------------> | server | > Host | +--------+ > +--------+ | ... > | iperf |---- > | client |---- Guest n > +--------+ | +--------+ > | | iperf | > ---------------> | server | > +--------+ > > Boot many guests from qemu with virtio network: > qemu ... -netdev tap,id=net_x \ > -device virtio-net-pci-non-transitional,\ > iommu_platform=on,mac=xx:xx:xx:xx:xx:xx,netdev=net_x > > Each guest acts as iperf server with commands below: > iperf3 -s -D -i 10 -p 8001 > iperf3 -s -D -i 10 -p 8002 > > The host as iperf client: > iperf3 -c guest_IP -p 8001 -i 30 -w 256k -P 20 -t 40000 > iperf3 -c guest_IP -p 8002 -i 30 -w 256k -P 20 -t 40000 > > After some time, the host loses connection to the guest, > the guest can send packet to the host, but can't receive > packet from host. > > It's more likely to happen if SWIOTLB is enabled in the guest, > allocating and freeing bounce buffer takes some CPU ticks, > copying from/to bounce buffer takes more CPU ticks, compared > with that there is no bounce buffer in the guest. > Once the rate of producing packets from the host approximates > the rate of receiveing packets in the guest, the guest would > loop in NAPI. > > receive packets --- > | | > v | > free buf virtnet_poll > | | > v | > add buf to avail ring --- > | > | need kick the host? > | NAPI continues > v > receive packets --- > | | > v | > free buf virtnet_poll > | | > v | > add buf to avail ring --- > | > v > ... ... > > On the other hand, the host fetches free buf from avail > ring, if the buf in the avail ring is not enough, the > host notifies the guest the event by writing the avail > idx read from avail ring to the event idx of used ring, > then the host goes to sleep, waiting for the kick signal > from the guest. > > Once the guest finds the host is waiting for kick singal > (in virtqueue_kick_prepare_split()), it kicks the host. > > The host may stall forever at the sequences below: > > Host Guest > ------------ ----------- > fetch buf, send packet receive packet --- > ... ... | > fetch buf, send packet add buf | > ... add buf virtnet_poll > buf not enough avail idx-> add buf | > read avail idx add buf | > add buf --- > receive packet --- > write event idx ... | > wait for kick add buf virtnet_poll > ... | > --- > no more packet, exit NAPI > > In the first loop of NAPI above, indicated in the range of > virtnet_poll above, the host is sending packets while the > guest is receiving packets and adding buffers. > step 1: The buf is not enough, for example, a big packet > needs 5 buf, but the available buf count is 3. > The host read current avail idx. > step 2: The guest adds some buf, then checks whether the > host is waiting for kick signal, not at this time. > The used ring is not empty, the guest continues > the second loop of NAPI. > step 3: The host writes the avail idx read from avail > ring to used ring as event idx via > virtio_queue_set_notification(q->rx_vq, 1). > step 4: At the end of the second loop of NAPI, recheck > whether kick is needed, as the event idx in the > used ring written by the host is beyound the > range of kick condition, the guest will not > send kick signal to the host. > > Fixes: 06b12970174 ("virtio-net: fix network stall under load") > Signed-off-by: Wencheng Yang <east.moutain.yang@gmail.com> > --- > > Changelog: > v7: > - Add function virtio_queue_set_notification_and_check() > - Restore the function sequence introduce in v6 > > v6: > - Take packed packed queue into cosideration > - Adjust function sequence to fix compilation issue > > v5: > - Modify return type of virtio_queue_set_notification() to > bool to indicate whether the guest has added some buffers > after last check of avail idx > - Loop in virtio_net_has_buffers() if the available buffers > are not sufficient and the guest has added some buffers. > - Revert patch "06b12970174" > - Update the subject > > v4: > - Correct spelling mistake in the subject > - Describe the issue that virtio-net is blocked at host side > > v3: > - Add virtio-net tag in the subject > - Refine commit log > > v2: > - Add SOB tag at the end of the commit message > - Place Fixes tag at the end of the commit message > > v1: > - Initial patch > > hw/net/virtio-net.c | 19 ++++++++----------- > hw/virtio/virtio.c | 39 ++++++++++++++++++++++++++++++++++++++ > include/hw/virtio/virtio.h | 1 + > 3 files changed, 48 insertions(+), 11 deletions(-) > > diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c > index 9c7e85caea..357c651d9b 100644 > --- a/hw/net/virtio-net.c > +++ b/hw/net/virtio-net.c > @@ -1642,18 +1642,15 @@ static bool virtio_net_can_receive(NetClientState *nc) > static int virtio_net_has_buffers(VirtIONetQueue *q, int bufsize) > { > VirtIONet *n = q->n; > - if (virtio_queue_empty(q->rx_vq) || > - (n->mergeable_rx_bufs && > - !virtqueue_avail_bytes(q->rx_vq, bufsize, 0))) { > - virtio_queue_set_notification(q->rx_vq, 1); > - > - /* To avoid a race condition where the guest has made some buffers > - * available after the above check but before notification was > - * enabled, check for available buffers again. > - */ > - if (virtio_queue_empty(q->rx_vq) || > + > + while (virtio_queue_empty(q->rx_vq) || > (n->mergeable_rx_bufs && > - !virtqueue_avail_bytes(q->rx_vq, bufsize, 0))) { > + !virtqueue_avail_bytes(q->rx_vq, bufsize, 0))) { > + /* guest may have made some buf, try again */ > + if (virtio_queue_set_notification_and_check(q->rx_vq, 1)) { > + virtio_queue_set_notification(q->rx_vq, 0); > + continue; > + } else { > return 0; > } > } > diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c > index 893a072c9d..b165764017 100644 > --- a/hw/virtio/virtio.c > +++ b/hw/virtio/virtio.c > @@ -668,6 +668,45 @@ static inline bool is_desc_avail(uint16_t flags, bool wrap_counter) > return (avail != used) && (avail == wrap_counter); > } > > +bool virtio_queue_set_notification_and_check(VirtQueue *vq, int enable) > +{ > + uint16_t shadow_idx; > + VRingPackedDesc desc; > + VRingMemoryRegionCaches *caches; > + > + vq->notification = enable; > + > + if (!vq->vring.desc) { > + return false; > + } > + > + if (virtio_vdev_has_feature(vq->vdev, VIRTIO_F_RING_PACKED)) { > + virtio_queue_packed_set_notification(vq, enable); > + > + if (enable) { > + caches = vring_get_region_caches(vq); > + if (!caches) { > + return false; > + } > + > + vring_packed_desc_read(vq->vdev, &desc, &caches->desc, > + vq->shadow_avail_idx, true); > + if (is_desc_avail(desc.flags, vq->shadow_avail_wrap_counter)) { > + return true; > + } > + } > + } else { > + shadow_idx = vq->shadow_avail_idx; > + virtio_queue_split_set_notification(vq, enable); > + > + if (enable) { > + return shadow_idx != vring_avail_idx(vq); > + } > + } > + > + return false; > +} Please document what this does. So this will return false if ring has any availabe buffers? Equivalent to: bool virtio_queue_set_notification_and_check(VirtQueue *vq, int enable) { virtio_queue_packed_set_notification(vq, enable); return virtio_queue_empty(vq); } or am I missing something? > + > /* Fetch avail_idx from VQ memory only when we really need to know if > * guest has added some buffers. > * Called within rcu_read_lock(). */ > diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h > index 7d5ffdc145..ed85023b87 100644 > --- a/include/hw/virtio/virtio.h > +++ b/include/hw/virtio/virtio.h > @@ -302,6 +302,7 @@ void virtio_notify_config(VirtIODevice *vdev); > > bool virtio_queue_get_notification(VirtQueue *vq); > void virtio_queue_set_notification(VirtQueue *vq, int enable); > +bool virtio_queue_set_notification_and_check(VirtQueue *vq, int enable); > > int virtio_queue_ready(VirtQueue *vq); > > -- > 2.39.0
> Please document what this does. okay, i will. > So this will return false if ring has any available buffers? > Equivalent to: > > bool virtio_queue_set_notification_and_check(VirtQueue *vq, int enable) > { > virtio_queue_packed_set_notification(vq, enable); > return virtio_queue_empty(vq); > } No, only when the *shadow_avail_idx *is changed shall the function return true, compared with the value seen by the host last time, else return false even if there are some buffers available in the queue, as the total size of the available buffers in the queue can't satisfy the request. It maybe better to pass only one arg to the function like this: bool virtio_queue_set_notification_and_check(VirtQueue *vq) { virtio_queue_packed_set_notification(vq, true); return shadow_avail_idx_changed()? true: false; } Thanks Michael a lot! On Mon, Jul 1, 2024 at 11:05 PM Michael S. Tsirkin <mst@redhat.com> wrote: > On Mon, Jul 01, 2024 at 10:00:17PM +0800, Wencheng Yang wrote: > > From: thomas <east.moutain.yang@gmail.com> > > > > Patch 06b12970174 ("virtio-net: fix network stall under load") > > added double-check to test whether the available buffer size > > can satisfy the request or not, in case the guest has added > > some buffers to the avail ring simultaneously after the first > > check. It will be lucky if the available buffer size becomes > > okay after the double-check, then the host can send the packet > > to the guest. If the buffer size still can't satisfy the request, > > even if the guest has added some buffers, viritio-net would > > stall at the host side forever. > > > > The patch checks whether the guest has added some buffers > > after last check of avail idx when the available buffers are > > not sufficient, if so then recheck the available buffers > > in the loop. > > > > The patch also reverts patch "06b12970174". > > > > The case below can reproduce the stall. > > > > Guest 0 > > +--------+ > > | iperf | > > ---------------> | server | > > Host | +--------+ > > +--------+ | ... > > | iperf |---- > > | client |---- Guest n > > +--------+ | +--------+ > > | | iperf | > > ---------------> | server | > > +--------+ > > > > Boot many guests from qemu with virtio network: > > qemu ... -netdev tap,id=net_x \ > > -device virtio-net-pci-non-transitional,\ > > iommu_platform=on,mac=xx:xx:xx:xx:xx:xx,netdev=net_x > > > > Each guest acts as iperf server with commands below: > > iperf3 -s -D -i 10 -p 8001 > > iperf3 -s -D -i 10 -p 8002 > > > > The host as iperf client: > > iperf3 -c guest_IP -p 8001 -i 30 -w 256k -P 20 -t 40000 > > iperf3 -c guest_IP -p 8002 -i 30 -w 256k -P 20 -t 40000 > > > > After some time, the host loses connection to the guest, > > the guest can send packet to the host, but can't receive > > packet from host. > > > > It's more likely to happen if SWIOTLB is enabled in the guest, > > allocating and freeing bounce buffer takes some CPU ticks, > > copying from/to bounce buffer takes more CPU ticks, compared > > with that there is no bounce buffer in the guest. > > Once the rate of producing packets from the host approximates > > the rate of receiveing packets in the guest, the guest would > > loop in NAPI. > > > > receive packets --- > > | | > > v | > > free buf virtnet_poll > > | | > > v | > > add buf to avail ring --- > > | > > | need kick the host? > > | NAPI continues > > v > > receive packets --- > > | | > > v | > > free buf virtnet_poll > > | | > > v | > > add buf to avail ring --- > > | > > v > > ... ... > > > > On the other hand, the host fetches free buf from avail > > ring, if the buf in the avail ring is not enough, the > > host notifies the guest the event by writing the avail > > idx read from avail ring to the event idx of used ring, > > then the host goes to sleep, waiting for the kick signal > > from the guest. > > > > Once the guest finds the host is waiting for kick singal > > (in virtqueue_kick_prepare_split()), it kicks the host. > > > > The host may stall forever at the sequences below: > > > > Host Guest > > ------------ ----------- > > fetch buf, send packet receive packet --- > > ... ... | > > fetch buf, send packet add buf | > > ... add buf virtnet_poll > > buf not enough avail idx-> add buf | > > read avail idx add buf | > > add buf --- > > receive packet --- > > write event idx ... | > > wait for kick add buf virtnet_poll > > ... | > > --- > > no more packet, exit NAPI > > > > In the first loop of NAPI above, indicated in the range of > > virtnet_poll above, the host is sending packets while the > > guest is receiving packets and adding buffers. > > step 1: The buf is not enough, for example, a big packet > > needs 5 buf, but the available buf count is 3. > > The host read current avail idx. > > step 2: The guest adds some buf, then checks whether the > > host is waiting for kick signal, not at this time. > > The used ring is not empty, the guest continues > > the second loop of NAPI. > > step 3: The host writes the avail idx read from avail > > ring to used ring as event idx via > > virtio_queue_set_notification(q->rx_vq, 1). > > step 4: At the end of the second loop of NAPI, recheck > > whether kick is needed, as the event idx in the > > used ring written by the host is beyound the > > range of kick condition, the guest will not > > send kick signal to the host. > > > > Fixes: 06b12970174 ("virtio-net: fix network stall under load") > > Signed-off-by: Wencheng Yang <east.moutain.yang@gmail.com> > > --- > > > > Changelog: > > v7: > > - Add function virtio_queue_set_notification_and_check() > > - Restore the function sequence introduce in v6 > > > > v6: > > - Take packed packed queue into cosideration > > - Adjust function sequence to fix compilation issue > > > > v5: > > - Modify return type of virtio_queue_set_notification() to > > bool to indicate whether the guest has added some buffers > > after last check of avail idx > > - Loop in virtio_net_has_buffers() if the available buffers > > are not sufficient and the guest has added some buffers. > > - Revert patch "06b12970174" > > - Update the subject > > > > v4: > > - Correct spelling mistake in the subject > > - Describe the issue that virtio-net is blocked at host side > > > > v3: > > - Add virtio-net tag in the subject > > - Refine commit log > > > > v2: > > - Add SOB tag at the end of the commit message > > - Place Fixes tag at the end of the commit message > > > > v1: > > - Initial patch > > > > hw/net/virtio-net.c | 19 ++++++++----------- > > hw/virtio/virtio.c | 39 ++++++++++++++++++++++++++++++++++++++ > > include/hw/virtio/virtio.h | 1 + > > 3 files changed, 48 insertions(+), 11 deletions(-) > > > > diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c > > index 9c7e85caea..357c651d9b 100644 > > --- a/hw/net/virtio-net.c > > +++ b/hw/net/virtio-net.c > > @@ -1642,18 +1642,15 @@ static bool > virtio_net_can_receive(NetClientState *nc) > > static int virtio_net_has_buffers(VirtIONetQueue *q, int bufsize) > > { > > VirtIONet *n = q->n; > > - if (virtio_queue_empty(q->rx_vq) || > > - (n->mergeable_rx_bufs && > > - !virtqueue_avail_bytes(q->rx_vq, bufsize, 0))) { > > - virtio_queue_set_notification(q->rx_vq, 1); > > - > > - /* To avoid a race condition where the guest has made some > buffers > > - * available after the above check but before notification was > > - * enabled, check for available buffers again. > > - */ > > - if (virtio_queue_empty(q->rx_vq) || > > + > > + while (virtio_queue_empty(q->rx_vq) || > > (n->mergeable_rx_bufs && > > - !virtqueue_avail_bytes(q->rx_vq, bufsize, 0))) { > > + !virtqueue_avail_bytes(q->rx_vq, bufsize, 0))) { > > + /* guest may have made some buf, try again */ > > + if (virtio_queue_set_notification_and_check(q->rx_vq, 1)) { > > + virtio_queue_set_notification(q->rx_vq, 0); > > + continue; > > + } else { > > return 0; > > } > > } > > diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c > > index 893a072c9d..b165764017 100644 > > --- a/hw/virtio/virtio.c > > +++ b/hw/virtio/virtio.c > > @@ -668,6 +668,45 @@ static inline bool is_desc_avail(uint16_t flags, > bool wrap_counter) > > return (avail != used) && (avail == wrap_counter); > > } > > > > +bool virtio_queue_set_notification_and_check(VirtQueue *vq, int enable) > > +{ > > + uint16_t shadow_idx; > > + VRingPackedDesc desc; > > + VRingMemoryRegionCaches *caches; > > + > > + vq->notification = enable; > > + > > + if (!vq->vring.desc) { > > + return false; > > + } > > + > > + if (virtio_vdev_has_feature(vq->vdev, VIRTIO_F_RING_PACKED)) { > > + virtio_queue_packed_set_notification(vq, enable); > > + > > + if (enable) { > > + caches = vring_get_region_caches(vq); > > + if (!caches) { > > + return false; > > + } > > + > > + vring_packed_desc_read(vq->vdev, &desc, &caches->desc, > > + vq->shadow_avail_idx, true); > > + if (is_desc_avail(desc.flags, > vq->shadow_avail_wrap_counter)) { > > + return true; > > + } > > + } > > + } else { > > + shadow_idx = vq->shadow_avail_idx; > > + virtio_queue_split_set_notification(vq, enable); > > + > > + if (enable) { > > + return shadow_idx != vring_avail_idx(vq); > > + } > > + } > > + > > + return false; > > +} > > Please document what this does. > So this will return false if ring has any availabe buffers? > Equivalent to: > > bool virtio_queue_set_notification_and_check(VirtQueue *vq, int enable) > { > virtio_queue_packed_set_notification(vq, enable); > return virtio_queue_empty(vq); > } > > > or am I missing something? > > > + > > /* Fetch avail_idx from VQ memory only when we really need to know if > > * guest has added some buffers. > > * Called within rcu_read_lock(). */ > > diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h > > index 7d5ffdc145..ed85023b87 100644 > > --- a/include/hw/virtio/virtio.h > > +++ b/include/hw/virtio/virtio.h > > @@ -302,6 +302,7 @@ void virtio_notify_config(VirtIODevice *vdev); > > > > bool virtio_queue_get_notification(VirtQueue *vq); > > void virtio_queue_set_notification(VirtQueue *vq, int enable); > > +bool virtio_queue_set_notification_and_check(VirtQueue *vq, int enable); > > > > int virtio_queue_ready(VirtQueue *vq); > > > > -- > > 2.39.0 > >
On Tue, Jul 02, 2024 at 01:18:15AM +0800, Yang Dongshan wrote: > > Please document what this does. > okay, i will. > > > So this will return false if ring has any available buffers? > > Equivalent to: > > > > bool virtio_queue_set_notification_and_check(VirtQueue *vq, int enable) > > { > > virtio_queue_packed_set_notification(vq, enable); > > return virtio_queue_empty(vq); > > } > > No, only when the shadow_avail_idx is changed shall the function return true, what does "changed" mean here? changed compared to what? > compared with the value seen by the host last time, else return false even if > there are some buffers available in the queue, as the total size of the > available > buffers in the queue can't satisfy the request. > > It maybe better to pass only one arg to the function like this: > bool virtio_queue_set_notification_and_check(VirtQueue *vq) > { > virtio_queue_packed_set_notification(vq, true); > > return shadow_avail_idx_changed()? true: false; > } > > Thanks Michael a lot! > > On Mon, Jul 1, 2024 at 11:05 PM Michael S. Tsirkin <mst@redhat.com> wrote: > > On Mon, Jul 01, 2024 at 10:00:17PM +0800, Wencheng Yang wrote: > > From: thomas <east.moutain.yang@gmail.com> > > > > Patch 06b12970174 ("virtio-net: fix network stall under load") > > added double-check to test whether the available buffer size > > can satisfy the request or not, in case the guest has added > > some buffers to the avail ring simultaneously after the first > > check. It will be lucky if the available buffer size becomes > > okay after the double-check, then the host can send the packet > > to the guest. If the buffer size still can't satisfy the request, > > even if the guest has added some buffers, viritio-net would > > stall at the host side forever. > > > > The patch checks whether the guest has added some buffers > > after last check of avail idx when the available buffers are > > not sufficient, if so then recheck the available buffers > > in the loop. > > > > The patch also reverts patch "06b12970174". > > > > The case below can reproduce the stall. > > > > Guest 0 > > +--------+ > > | iperf | > > ---------------> | server | > > Host | +--------+ > > +--------+ | ... > > | iperf |---- > > | client |---- Guest n > > +--------+ | +--------+ > > | | iperf | > > ---------------> | server | > > +--------+ > > > > Boot many guests from qemu with virtio network: > > qemu ... -netdev tap,id=net_x \ > > -device virtio-net-pci-non-transitional,\ > > iommu_platform=on,mac=xx:xx:xx:xx:xx:xx,netdev=net_x > > > > Each guest acts as iperf server with commands below: > > iperf3 -s -D -i 10 -p 8001 > > iperf3 -s -D -i 10 -p 8002 > > > > The host as iperf client: > > iperf3 -c guest_IP -p 8001 -i 30 -w 256k -P 20 -t 40000 > > iperf3 -c guest_IP -p 8002 -i 30 -w 256k -P 20 -t 40000 > > > > After some time, the host loses connection to the guest, > > the guest can send packet to the host, but can't receive > > packet from host. > > > > It's more likely to happen if SWIOTLB is enabled in the guest, > > allocating and freeing bounce buffer takes some CPU ticks, > > copying from/to bounce buffer takes more CPU ticks, compared > > with that there is no bounce buffer in the guest. > > Once the rate of producing packets from the host approximates > > the rate of receiveing packets in the guest, the guest would > > loop in NAPI. > > > > receive packets --- > > | | > > v | > > free buf virtnet_poll > > | | > > v | > > add buf to avail ring --- > > | > > | need kick the host? > > | NAPI continues > > v > > receive packets --- > > | | > > v | > > free buf virtnet_poll > > | | > > v | > > add buf to avail ring --- > > | > > v > > ... ... > > > > On the other hand, the host fetches free buf from avail > > ring, if the buf in the avail ring is not enough, the > > host notifies the guest the event by writing the avail > > idx read from avail ring to the event idx of used ring, > > then the host goes to sleep, waiting for the kick signal > > from the guest. > > > > Once the guest finds the host is waiting for kick singal > > (in virtqueue_kick_prepare_split()), it kicks the host. > > > > The host may stall forever at the sequences below: > > > > Host Guest > > ------------ ----------- > > fetch buf, send packet receive packet --- > > ... ... | > > fetch buf, send packet add buf | > > ... add buf virtnet_poll > > buf not enough avail idx-> add buf | > > read avail idx add buf | > > add buf --- > > receive packet --- > > write event idx ... | > > wait for kick add buf virtnet_poll > > ... | > > --- > > no more packet, exit NAPI > > > > In the first loop of NAPI above, indicated in the range of > > virtnet_poll above, the host is sending packets while the > > guest is receiving packets and adding buffers. > > step 1: The buf is not enough, for example, a big packet > > needs 5 buf, but the available buf count is 3. > > The host read current avail idx. > > step 2: The guest adds some buf, then checks whether the > > host is waiting for kick signal, not at this time. > > The used ring is not empty, the guest continues > > the second loop of NAPI. > > step 3: The host writes the avail idx read from avail > > ring to used ring as event idx via > > virtio_queue_set_notification(q->rx_vq, 1). > > step 4: At the end of the second loop of NAPI, recheck > > whether kick is needed, as the event idx in the > > used ring written by the host is beyound the > > range of kick condition, the guest will not > > send kick signal to the host. > > > > Fixes: 06b12970174 ("virtio-net: fix network stall under load") > > Signed-off-by: Wencheng Yang <east.moutain.yang@gmail.com> > > --- > > > > Changelog: > > v7: > > - Add function virtio_queue_set_notification_and_check() > > - Restore the function sequence introduce in v6 > > > > v6: > > - Take packed packed queue into cosideration > > - Adjust function sequence to fix compilation issue > > > > v5: > > - Modify return type of virtio_queue_set_notification() to > > bool to indicate whether the guest has added some buffers > > after last check of avail idx > > - Loop in virtio_net_has_buffers() if the available buffers > > are not sufficient and the guest has added some buffers. > > - Revert patch "06b12970174" > > - Update the subject > > > > v4: > > - Correct spelling mistake in the subject > > - Describe the issue that virtio-net is blocked at host side > > > > v3: > > - Add virtio-net tag in the subject > > - Refine commit log > > > > v2: > > - Add SOB tag at the end of the commit message > > - Place Fixes tag at the end of the commit message > > > > v1: > > - Initial patch > > > > hw/net/virtio-net.c | 19 ++++++++----------- > > hw/virtio/virtio.c | 39 ++++++++++++++++++++++++++++++++++++++ > > include/hw/virtio/virtio.h | 1 + > > 3 files changed, 48 insertions(+), 11 deletions(-) > > > > diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c > > index 9c7e85caea..357c651d9b 100644 > > --- a/hw/net/virtio-net.c > > +++ b/hw/net/virtio-net.c > > @@ -1642,18 +1642,15 @@ static bool virtio_net_can_receive(NetClientState > *nc) > > static int virtio_net_has_buffers(VirtIONetQueue *q, int bufsize) > > { > > VirtIONet *n = q->n; > > - if (virtio_queue_empty(q->rx_vq) || > > - (n->mergeable_rx_bufs && > > - !virtqueue_avail_bytes(q->rx_vq, bufsize, 0))) { > > - virtio_queue_set_notification(q->rx_vq, 1); > > - > > - /* To avoid a race condition where the guest has made some > buffers > > - * available after the above check but before notification was > > - * enabled, check for available buffers again. > > - */ > > - if (virtio_queue_empty(q->rx_vq) || > > + > > + while (virtio_queue_empty(q->rx_vq) || > > (n->mergeable_rx_bufs && > > - !virtqueue_avail_bytes(q->rx_vq, bufsize, 0))) { > > + !virtqueue_avail_bytes(q->rx_vq, bufsize, 0))) { > > + /* guest may have made some buf, try again */ > > + if (virtio_queue_set_notification_and_check(q->rx_vq, 1)) { > > + virtio_queue_set_notification(q->rx_vq, 0); > > + continue; > > + } else { > > return 0; > > } > > } > > diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c > > index 893a072c9d..b165764017 100644 > > --- a/hw/virtio/virtio.c > > +++ b/hw/virtio/virtio.c > > @@ -668,6 +668,45 @@ static inline bool is_desc_avail(uint16_t flags, > bool wrap_counter) > > return (avail != used) && (avail == wrap_counter); > > } > > > > +bool virtio_queue_set_notification_and_check(VirtQueue *vq, int enable) > > +{ > > + uint16_t shadow_idx; > > + VRingPackedDesc desc; > > + VRingMemoryRegionCaches *caches; > > + > > + vq->notification = enable; > > + > > + if (!vq->vring.desc) { > > + return false; > > + } > > + > > + if (virtio_vdev_has_feature(vq->vdev, VIRTIO_F_RING_PACKED)) { > > + virtio_queue_packed_set_notification(vq, enable); > > + > > + if (enable) { > > + caches = vring_get_region_caches(vq); > > + if (!caches) { > > + return false; > > + } > > + > > + vring_packed_desc_read(vq->vdev, &desc, &caches->desc, > > + vq->shadow_avail_idx, true); > > + if (is_desc_avail(desc.flags, vq-> > shadow_avail_wrap_counter)) { > > + return true; > > + } > > + } > > + } else { > > + shadow_idx = vq->shadow_avail_idx; > > + virtio_queue_split_set_notification(vq, enable); > > + > > + if (enable) { > > + return shadow_idx != vring_avail_idx(vq); > > + } > > + } > > + > > + return false; > > +} > > Please document what this does. > So this will return false if ring has any availabe buffers? > Equivalent to: > > bool virtio_queue_set_notification_and_check(VirtQueue *vq, int enable) > { > virtio_queue_packed_set_notification(vq, enable); > return virtio_queue_empty(vq); > } > > > or am I missing something? > > > + > > /* Fetch avail_idx from VQ memory only when we really need to know if > > * guest has added some buffers. > > * Called within rcu_read_lock(). */ > > diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h > > index 7d5ffdc145..ed85023b87 100644 > > --- a/include/hw/virtio/virtio.h > > +++ b/include/hw/virtio/virtio.h > > @@ -302,6 +302,7 @@ void virtio_notify_config(VirtIODevice *vdev); > > > > bool virtio_queue_get_notification(VirtQueue *vq); > > void virtio_queue_set_notification(VirtQueue *vq, int enable); > > +bool virtio_queue_set_notification_and_check(VirtQueue *vq, int enable); > > > > int virtio_queue_ready(VirtQueue *vq); > > > > -- > > 2.39.0 > >
> what does "changed" mean here? changed compared to what? For a split queue, if the shadow_avail_idx synced from avail ring idx by *vring_avail_idx(vq) last time doesn't equal the current value of avail ring idx.* *vq->shadow_avail_idx **!= vring_avail_idx(vq);* For packed queue, the logic is similar, if vq->shadow_avail_idx becomes available, it means the guest has added buf at the slot. *vring_packed_desc_read(vq->vdev, &desc, &caches->desc,* *vq->shadow_avail_idx, true);* *if (is_desc_avail(desc.flags, vq-> **shadow_avail_wrap_counter))* * return true;* On Tue, Jul 2, 2024 at 2:46 AM Michael S. Tsirkin <mst@redhat.com> wrote: > On Tue, Jul 02, 2024 at 01:18:15AM +0800, Yang Dongshan wrote: > > > Please document what this does. > > okay, i will. > > > > > So this will return false if ring has any available buffers? > > > Equivalent to: > > > > > > bool virtio_queue_set_notification_and_check(VirtQueue *vq, int enable) > > > { > > > virtio_queue_packed_set_notification(vq, enable); > > > return virtio_queue_empty(vq); > > > } > > > > No, only when the shadow_avail_idx is changed shall the function return > true, > > > what does "changed" mean here? changed compared to what? > > > compared with the value seen by the host last time, else return false > even if > > there are some buffers available in the queue, as the total size of the > > available > > buffers in the queue can't satisfy the request. > > > > It maybe better to pass only one arg to the function like this: > > bool virtio_queue_set_notification_and_check(VirtQueue *vq) > > { > > virtio_queue_packed_set_notification(vq, true); > > > > return shadow_avail_idx_changed()? true: false; > > } > > > > Thanks Michael a lot! > > > > On Mon, Jul 1, 2024 at 11:05 PM Michael S. Tsirkin <mst@redhat.com> > wrote: > > > > On Mon, Jul 01, 2024 at 10:00:17PM +0800, Wencheng Yang wrote: > > > From: thomas <east.moutain.yang@gmail.com> > > > > > > Patch 06b12970174 ("virtio-net: fix network stall under load") > > > added double-check to test whether the available buffer size > > > can satisfy the request or not, in case the guest has added > > > some buffers to the avail ring simultaneously after the first > > > check. It will be lucky if the available buffer size becomes > > > okay after the double-check, then the host can send the packet > > > to the guest. If the buffer size still can't satisfy the request, > > > even if the guest has added some buffers, viritio-net would > > > stall at the host side forever. > > > > > > The patch checks whether the guest has added some buffers > > > after last check of avail idx when the available buffers are > > > not sufficient, if so then recheck the available buffers > > > in the loop. > > > > > > The patch also reverts patch "06b12970174". > > > > > > The case below can reproduce the stall. > > > > > > Guest 0 > > > +--------+ > > > | iperf | > > > ---------------> | server | > > > Host | +--------+ > > > +--------+ | ... > > > | iperf |---- > > > | client |---- Guest n > > > +--------+ | +--------+ > > > | | iperf | > > > ---------------> | server | > > > +--------+ > > > > > > Boot many guests from qemu with virtio network: > > > qemu ... -netdev tap,id=net_x \ > > > -device virtio-net-pci-non-transitional,\ > > > iommu_platform=on,mac=xx:xx:xx:xx:xx:xx,netdev=net_x > > > > > > Each guest acts as iperf server with commands below: > > > iperf3 -s -D -i 10 -p 8001 > > > iperf3 -s -D -i 10 -p 8002 > > > > > > The host as iperf client: > > > iperf3 -c guest_IP -p 8001 -i 30 -w 256k -P 20 -t 40000 > > > iperf3 -c guest_IP -p 8002 -i 30 -w 256k -P 20 -t 40000 > > > > > > After some time, the host loses connection to the guest, > > > the guest can send packet to the host, but can't receive > > > packet from host. > > > > > > It's more likely to happen if SWIOTLB is enabled in the guest, > > > allocating and freeing bounce buffer takes some CPU ticks, > > > copying from/to bounce buffer takes more CPU ticks, compared > > > with that there is no bounce buffer in the guest. > > > Once the rate of producing packets from the host approximates > > > the rate of receiveing packets in the guest, the guest would > > > loop in NAPI. > > > > > > receive packets --- > > > | | > > > v | > > > free buf virtnet_poll > > > | | > > > v | > > > add buf to avail ring --- > > > | > > > | need kick the host? > > > | NAPI continues > > > v > > > receive packets --- > > > | | > > > v | > > > free buf virtnet_poll > > > | | > > > v | > > > add buf to avail ring --- > > > | > > > v > > > ... ... > > > > > > On the other hand, the host fetches free buf from avail > > > ring, if the buf in the avail ring is not enough, the > > > host notifies the guest the event by writing the avail > > > idx read from avail ring to the event idx of used ring, > > > then the host goes to sleep, waiting for the kick signal > > > from the guest. > > > > > > Once the guest finds the host is waiting for kick singal > > > (in virtqueue_kick_prepare_split()), it kicks the host. > > > > > > The host may stall forever at the sequences below: > > > > > > Host Guest > > > ------------ ----------- > > > fetch buf, send packet receive packet --- > > > ... ... | > > > fetch buf, send packet add buf | > > > ... add buf virtnet_poll > > > buf not enough avail idx-> add buf | > > > read avail idx add buf | > > > add buf --- > > > receive packet --- > > > write event idx ... | > > > wait for kick add buf virtnet_poll > > > ... | > > > --- > > > no more packet, exit NAPI > > > > > > In the first loop of NAPI above, indicated in the range of > > > virtnet_poll above, the host is sending packets while the > > > guest is receiving packets and adding buffers. > > > step 1: The buf is not enough, for example, a big packet > > > needs 5 buf, but the available buf count is 3. > > > The host read current avail idx. > > > step 2: The guest adds some buf, then checks whether the > > > host is waiting for kick signal, not at this time. > > > The used ring is not empty, the guest continues > > > the second loop of NAPI. > > > step 3: The host writes the avail idx read from avail > > > ring to used ring as event idx via > > > virtio_queue_set_notification(q->rx_vq, 1). > > > step 4: At the end of the second loop of NAPI, recheck > > > whether kick is needed, as the event idx in the > > > used ring written by the host is beyound the > > > range of kick condition, the guest will not > > > send kick signal to the host. > > > > > > Fixes: 06b12970174 ("virtio-net: fix network stall under load") > > > Signed-off-by: Wencheng Yang <east.moutain.yang@gmail.com> > > > --- > > > > > > Changelog: > > > v7: > > > - Add function virtio_queue_set_notification_and_check() > > > - Restore the function sequence introduce in v6 > > > > > > v6: > > > - Take packed packed queue into cosideration > > > - Adjust function sequence to fix compilation issue > > > > > > v5: > > > - Modify return type of virtio_queue_set_notification() to > > > bool to indicate whether the guest has added some buffers > > > after last check of avail idx > > > - Loop in virtio_net_has_buffers() if the available buffers > > > are not sufficient and the guest has added some buffers. > > > - Revert patch "06b12970174" > > > - Update the subject > > > > > > v4: > > > - Correct spelling mistake in the subject > > > - Describe the issue that virtio-net is blocked at host side > > > > > > v3: > > > - Add virtio-net tag in the subject > > > - Refine commit log > > > > > > v2: > > > - Add SOB tag at the end of the commit message > > > - Place Fixes tag at the end of the commit message > > > > > > v1: > > > - Initial patch > > > > > > hw/net/virtio-net.c | 19 ++++++++----------- > > > hw/virtio/virtio.c | 39 > ++++++++++++++++++++++++++++++++++++++ > > > include/hw/virtio/virtio.h | 1 + > > > 3 files changed, 48 insertions(+), 11 deletions(-) > > > > > > diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c > > > index 9c7e85caea..357c651d9b 100644 > > > --- a/hw/net/virtio-net.c > > > +++ b/hw/net/virtio-net.c > > > @@ -1642,18 +1642,15 @@ static bool > virtio_net_can_receive(NetClientState > > *nc) > > > static int virtio_net_has_buffers(VirtIONetQueue *q, int bufsize) > > > { > > > VirtIONet *n = q->n; > > > - if (virtio_queue_empty(q->rx_vq) || > > > - (n->mergeable_rx_bufs && > > > - !virtqueue_avail_bytes(q->rx_vq, bufsize, 0))) { > > > - virtio_queue_set_notification(q->rx_vq, 1); > > > - > > > - /* To avoid a race condition where the guest has made some > > buffers > > > - * available after the above check but before > notification was > > > - * enabled, check for available buffers again. > > > - */ > > > - if (virtio_queue_empty(q->rx_vq) || > > > + > > > + while (virtio_queue_empty(q->rx_vq) || > > > (n->mergeable_rx_bufs && > > > - !virtqueue_avail_bytes(q->rx_vq, bufsize, 0))) { > > > + !virtqueue_avail_bytes(q->rx_vq, bufsize, 0))) { > > > + /* guest may have made some buf, try again */ > > > + if (virtio_queue_set_notification_and_check(q->rx_vq, 1)) > { > > > + virtio_queue_set_notification(q->rx_vq, 0); > > > + continue; > > > + } else { > > > return 0; > > > } > > > } > > > diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c > > > index 893a072c9d..b165764017 100644 > > > --- a/hw/virtio/virtio.c > > > +++ b/hw/virtio/virtio.c > > > @@ -668,6 +668,45 @@ static inline bool is_desc_avail(uint16_t > flags, > > bool wrap_counter) > > > return (avail != used) && (avail == wrap_counter); > > > } > > > > > > +bool virtio_queue_set_notification_and_check(VirtQueue *vq, int > enable) > > > +{ > > > + uint16_t shadow_idx; > > > + VRingPackedDesc desc; > > > + VRingMemoryRegionCaches *caches; > > > + > > > + vq->notification = enable; > > > + > > > + if (!vq->vring.desc) { > > > + return false; > > > + } > > > + > > > + if (virtio_vdev_has_feature(vq->vdev, VIRTIO_F_RING_PACKED)) { > > > + virtio_queue_packed_set_notification(vq, enable); > > > + > > > + if (enable) { > > > + caches = vring_get_region_caches(vq); > > > + if (!caches) { > > > + return false; > > > + } > > > + > > > + vring_packed_desc_read(vq->vdev, &desc, &caches->desc, > > > + vq->shadow_avail_idx, true); > > > + if (is_desc_avail(desc.flags, vq-> > > shadow_avail_wrap_counter)) { > > > + return true; > > > + } > > > + } > > > + } else { > > > + shadow_idx = vq->shadow_avail_idx; > > > + virtio_queue_split_set_notification(vq, enable); > > > + > > > + if (enable) { > > > + return shadow_idx != vring_avail_idx(vq); > > > + } > > > + } > > > + > > > + return false; > > > +} > > > > Please document what this does. > > So this will return false if ring has any availabe buffers? > > Equivalent to: > > > > bool virtio_queue_set_notification_and_check(VirtQueue *vq, int > enable) > > { > > virtio_queue_packed_set_notification(vq, enable); > > return virtio_queue_empty(vq); > > } > > > > > > or am I missing something? > > > > > + > > > /* Fetch avail_idx from VQ memory only when we really need to > know if > > > * guest has added some buffers. > > > * Called within rcu_read_lock(). */ > > > diff --git a/include/hw/virtio/virtio.h > b/include/hw/virtio/virtio.h > > > index 7d5ffdc145..ed85023b87 100644 > > > --- a/include/hw/virtio/virtio.h > > > +++ b/include/hw/virtio/virtio.h > > > @@ -302,6 +302,7 @@ void virtio_notify_config(VirtIODevice *vdev); > > > > > > bool virtio_queue_get_notification(VirtQueue *vq); > > > void virtio_queue_set_notification(VirtQueue *vq, int enable); > > > +bool virtio_queue_set_notification_and_check(VirtQueue *vq, int > enable); > > > > > > int virtio_queue_ready(VirtQueue *vq); > > > > > > -- > > > 2.39.0 > > > > > >
On Tue, Jul 02, 2024 at 07:45:31AM +0800, Yang Dongshan wrote: > > what does "changed" mean here? changed compared to what? > For a split queue, if the shadow_avail_idx synced from avail ring idx > by vring_avail_idx(vq) last time doesn't equal the current value of avail ring > idx. > > vq->shadow_avail_idx != vring_avail_idx(vq); > > For packed queue, the logic is similar, if vq->shadow_avail_idx > > becomes available, it means the guest has added buf at the slot. > > vring_packed_desc_read(vq->vdev, &desc, &caches->desc, > > vq->shadow_avail_idx, true); > > if (is_desc_avail(desc.flags, vq-> shadow_avail_wrap_counter)) > > return true; > > This answer does not make sense from API POV. My suggestion: change virtqueue_get_avail_bytes to return the shadow in an opaque unsigned value. add virtqueue_poll that gets this opaque and tells us whether any new buffers became available in the queue since that value was returned. accordingly, virtio_queue_set_notification_and_check will accept this opaque value and check avail buffers against it. > On Tue, Jul 2, 2024 at 2:46 AM Michael S. Tsirkin <mst@redhat.com> wrote: > > On Tue, Jul 02, 2024 at 01:18:15AM +0800, Yang Dongshan wrote: > > > Please document what this does. > > okay, i will. > > > > > So this will return false if ring has any available buffers? > > > Equivalent to: > > > > > > bool virtio_queue_set_notification_and_check(VirtQueue *vq, int enable) > > > { > > > virtio_queue_packed_set_notification(vq, enable); > > > return virtio_queue_empty(vq); > > > } > > > > No, only when the shadow_avail_idx is changed shall the function return > true, > > > what does "changed" mean here? changed compared to what? > > > compared with the value seen by the host last time, else return false > even if > > there are some buffers available in the queue, as the total size of the > > available > > buffers in the queue can't satisfy the request. > > > > It maybe better to pass only one arg to the function like this: > > bool virtio_queue_set_notification_and_check(VirtQueue *vq) > > { > > virtio_queue_packed_set_notification(vq, true); > > > > return shadow_avail_idx_changed()? true: false; > > } > > > > Thanks Michael a lot! > > > > On Mon, Jul 1, 2024 at 11:05 PM Michael S. Tsirkin <mst@redhat.com> > wrote: > > > > On Mon, Jul 01, 2024 at 10:00:17PM +0800, Wencheng Yang wrote: > > > From: thomas <east.moutain.yang@gmail.com> > > > > > > Patch 06b12970174 ("virtio-net: fix network stall under load") > > > added double-check to test whether the available buffer size > > > can satisfy the request or not, in case the guest has added > > > some buffers to the avail ring simultaneously after the first > > > check. It will be lucky if the available buffer size becomes > > > okay after the double-check, then the host can send the packet > > > to the guest. If the buffer size still can't satisfy the request, > > > even if the guest has added some buffers, viritio-net would > > > stall at the host side forever. > > > > > > The patch checks whether the guest has added some buffers > > > after last check of avail idx when the available buffers are > > > not sufficient, if so then recheck the available buffers > > > in the loop. > > > > > > The patch also reverts patch "06b12970174". > > > > > > The case below can reproduce the stall. > > > > > > Guest 0 > > > +--------+ > > > | iperf | > > > ---------------> | server | > > > Host | +--------+ > > > +--------+ | ... > > > | iperf |---- > > > | client |---- Guest n > > > +--------+ | +--------+ > > > | | iperf | > > > ---------------> | server | > > > +--------+ > > > > > > Boot many guests from qemu with virtio network: > > > qemu ... -netdev tap,id=net_x \ > > > -device virtio-net-pci-non-transitional,\ > > > iommu_platform=on,mac=xx:xx:xx:xx:xx:xx,netdev=net_x > > > > > > Each guest acts as iperf server with commands below: > > > iperf3 -s -D -i 10 -p 8001 > > > iperf3 -s -D -i 10 -p 8002 > > > > > > The host as iperf client: > > > iperf3 -c guest_IP -p 8001 -i 30 -w 256k -P 20 -t 40000 > > > iperf3 -c guest_IP -p 8002 -i 30 -w 256k -P 20 -t 40000 > > > > > > After some time, the host loses connection to the guest, > > > the guest can send packet to the host, but can't receive > > > packet from host. > > > > > > It's more likely to happen if SWIOTLB is enabled in the guest, > > > allocating and freeing bounce buffer takes some CPU ticks, > > > copying from/to bounce buffer takes more CPU ticks, compared > > > with that there is no bounce buffer in the guest. > > > Once the rate of producing packets from the host approximates > > > the rate of receiveing packets in the guest, the guest would > > > loop in NAPI. > > > > > > receive packets --- > > > | | > > > v | > > > free buf virtnet_poll > > > | | > > > v | > > > add buf to avail ring --- > > > | > > > | need kick the host? > > > | NAPI continues > > > v > > > receive packets --- > > > | | > > > v | > > > free buf virtnet_poll > > > | | > > > v | > > > add buf to avail ring --- > > > | > > > v > > > ... ... > > > > > > On the other hand, the host fetches free buf from avail > > > ring, if the buf in the avail ring is not enough, the > > > host notifies the guest the event by writing the avail > > > idx read from avail ring to the event idx of used ring, > > > then the host goes to sleep, waiting for the kick signal > > > from the guest. > > > > > > Once the guest finds the host is waiting for kick singal > > > (in virtqueue_kick_prepare_split()), it kicks the host. > > > > > > The host may stall forever at the sequences below: > > > > > > Host Guest > > > ------------ ----------- > > > fetch buf, send packet receive packet --- > > > ... ... | > > > fetch buf, send packet add buf | > > > ... add buf virtnet_poll > > > buf not enough avail idx-> add buf | > > > read avail idx add buf | > > > add buf --- > > > receive packet --- > > > write event idx ... | > > > wait for kick add buf virtnet_poll > > > ... | > > > --- > > > no more packet, exit NAPI > > > > > > In the first loop of NAPI above, indicated in the range of > > > virtnet_poll above, the host is sending packets while the > > > guest is receiving packets and adding buffers. > > > step 1: The buf is not enough, for example, a big packet > > > needs 5 buf, but the available buf count is 3. > > > The host read current avail idx. > > > step 2: The guest adds some buf, then checks whether the > > > host is waiting for kick signal, not at this time. > > > The used ring is not empty, the guest continues > > > the second loop of NAPI. > > > step 3: The host writes the avail idx read from avail > > > ring to used ring as event idx via > > > virtio_queue_set_notification(q->rx_vq, 1). > > > step 4: At the end of the second loop of NAPI, recheck > > > whether kick is needed, as the event idx in the > > > used ring written by the host is beyound the > > > range of kick condition, the guest will not > > > send kick signal to the host. > > > > > > Fixes: 06b12970174 ("virtio-net: fix network stall under load") > > > Signed-off-by: Wencheng Yang <east.moutain.yang@gmail.com> > > > --- > > > > > > Changelog: > > > v7: > > > - Add function virtio_queue_set_notification_and_check() > > > - Restore the function sequence introduce in v6 > > > > > > v6: > > > - Take packed packed queue into cosideration > > > - Adjust function sequence to fix compilation issue > > > > > > v5: > > > - Modify return type of virtio_queue_set_notification() to > > > bool to indicate whether the guest has added some buffers > > > after last check of avail idx > > > - Loop in virtio_net_has_buffers() if the available buffers > > > are not sufficient and the guest has added some buffers. > > > - Revert patch "06b12970174" > > > - Update the subject > > > > > > v4: > > > - Correct spelling mistake in the subject > > > - Describe the issue that virtio-net is blocked at host side > > > > > > v3: > > > - Add virtio-net tag in the subject > > > - Refine commit log > > > > > > v2: > > > - Add SOB tag at the end of the commit message > > > - Place Fixes tag at the end of the commit message > > > > > > v1: > > > - Initial patch > > > > > > hw/net/virtio-net.c | 19 ++++++++----------- > > > hw/virtio/virtio.c | 39 > ++++++++++++++++++++++++++++++++++++++ > > > include/hw/virtio/virtio.h | 1 + > > > 3 files changed, 48 insertions(+), 11 deletions(-) > > > > > > diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c > > > index 9c7e85caea..357c651d9b 100644 > > > --- a/hw/net/virtio-net.c > > > +++ b/hw/net/virtio-net.c > > > @@ -1642,18 +1642,15 @@ static bool virtio_net_can_receive > (NetClientState > > *nc) > > > static int virtio_net_has_buffers(VirtIONetQueue *q, int bufsize) > > > { > > > VirtIONet *n = q->n; > > > - if (virtio_queue_empty(q->rx_vq) || > > > - (n->mergeable_rx_bufs && > > > - !virtqueue_avail_bytes(q->rx_vq, bufsize, 0))) { > > > - virtio_queue_set_notification(q->rx_vq, 1); > > > - > > > - /* To avoid a race condition where the guest has made some > > buffers > > > - * available after the above check but before notification > was > > > - * enabled, check for available buffers again. > > > - */ > > > - if (virtio_queue_empty(q->rx_vq) || > > > + > > > + while (virtio_queue_empty(q->rx_vq) || > > > (n->mergeable_rx_bufs && > > > - !virtqueue_avail_bytes(q->rx_vq, bufsize, 0))) { > > > + !virtqueue_avail_bytes(q->rx_vq, bufsize, 0))) { > > > + /* guest may have made some buf, try again */ > > > + if (virtio_queue_set_notification_and_check(q->rx_vq, 1)) > { > > > + virtio_queue_set_notification(q->rx_vq, 0); > > > + continue; > > > + } else { > > > return 0; > > > } > > > } > > > diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c > > > index 893a072c9d..b165764017 100644 > > > --- a/hw/virtio/virtio.c > > > +++ b/hw/virtio/virtio.c > > > @@ -668,6 +668,45 @@ static inline bool is_desc_avail(uint16_t > flags, > > bool wrap_counter) > > > return (avail != used) && (avail == wrap_counter); > > > } > > > > > > +bool virtio_queue_set_notification_and_check(VirtQueue *vq, int > enable) > > > +{ > > > + uint16_t shadow_idx; > > > + VRingPackedDesc desc; > > > + VRingMemoryRegionCaches *caches; > > > + > > > + vq->notification = enable; > > > + > > > + if (!vq->vring.desc) { > > > + return false; > > > + } > > > + > > > + if (virtio_vdev_has_feature(vq->vdev, VIRTIO_F_RING_PACKED)) { > > > + virtio_queue_packed_set_notification(vq, enable); > > > + > > > + if (enable) { > > > + caches = vring_get_region_caches(vq); > > > + if (!caches) { > > > + return false; > > > + } > > > + > > > + vring_packed_desc_read(vq->vdev, &desc, &caches->desc, > > > + vq->shadow_avail_idx, true); > > > + if (is_desc_avail(desc.flags, vq-> > > shadow_avail_wrap_counter)) { > > > + return true; > > > + } > > > + } > > > + } else { > > > + shadow_idx = vq->shadow_avail_idx; > > > + virtio_queue_split_set_notification(vq, enable); > > > + > > > + if (enable) { > > > + return shadow_idx != vring_avail_idx(vq); > > > + } > > > + } > > > + > > > + return false; > > > +} > > > > Please document what this does. > > So this will return false if ring has any availabe buffers? > > Equivalent to: > > > > bool virtio_queue_set_notification_and_check(VirtQueue *vq, int > enable) > > { > > virtio_queue_packed_set_notification(vq, enable); > > return virtio_queue_empty(vq); > > } > > > > > > or am I missing something? > > > > > + > > > /* Fetch avail_idx from VQ memory only when we really need to know > if > > > * guest has added some buffers. > > > * Called within rcu_read_lock(). */ > > > diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/ > virtio.h > > > index 7d5ffdc145..ed85023b87 100644 > > > --- a/include/hw/virtio/virtio.h > > > +++ b/include/hw/virtio/virtio.h > > > @@ -302,6 +302,7 @@ void virtio_notify_config(VirtIODevice *vdev); > > > > > > bool virtio_queue_get_notification(VirtQueue *vq); > > > void virtio_queue_set_notification(VirtQueue *vq, int enable); > > > +bool virtio_queue_set_notification_and_check(VirtQueue *vq, int > enable); > > > > > > int virtio_queue_ready(VirtQueue *vq); > > > > > > -- > > > 2.39.0 > > > > > >
> This answer does not make sense from API POV. The core logic of function virtio_queue_set_notification_and_check() actually is a copy of function vhost_enable_notify() from vhost.c in kernel. > > > +bool virtio_queue_set_notification_and_check(VirtQueue *vq, int enable) > > > +{ > > > + uint16_t shadow_idx; > > > + VRingPackedDesc desc; > > > + VRingMemoryRegionCaches *caches; > > > + > > > + vq->notification = enable; > > > + > > > + if (!vq->vring.desc) { > > > + return false; > > > + } > > > + > > > + if (virtio_vdev_has_feature(vq->vdev, VIRTIO_F_RING_PACKED)) { > > > + virtio_queue_packed_set_notification(vq, enable); > > > + > > > + if (enable) { > > > + caches = vring_get_region_caches(vq); > > > + if (!caches) { > > > + return false; > > > + } > > > + > > > + vring_packed_desc_read(vq->vdev, &desc, &caches->desc, > > > + vq->shadow_avail_idx, true); > > > + if (is_desc_avail(desc.flags, vq-> > > shadow_avail_wrap_counter)) { > > > + return true; > > > + } > > > + } > > > + } else { > > > + shadow_idx = vq->shadow_avail_idx; > > > + virtio_queue_split_set_notification(vq, enable); > > > + > > > + if (enable) { > > > + return shadow_idx != vring_avail_idx(vq); > > > + } > > > + } > > > + > > > + return false; > > > +} // vhost.c bool vhost_enable_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq) { ... r = vhost_update_avail_event(vq, vq->avail_idx); ... r = vhost_get_avail_idx(vq, &avail_idx); return vhost16_to_cpu(vq, avail_idx) != vq->avail_idx; } > My suggestion: > change virtqueue_get_avail_bytes to return the shadow > in an opaque unsigned value. virtio_serial_guest_ready() is referenced by: virtio_serial_guest_ready() // virtio-serial-bus.c get_request_size() // virtio-rng.c virtqueue_avail_bytes() // virtio.c Change the return type of virtqueue_get_avail_bytes() from void to unsigned, it seems okay. > add virtqueue_poll that gets this opaque and tells us whether any new > buffers became available in the queue since that value >was returned. I'm not clear about the purpose of virtqueue_poll(), when will the function return? Do you mean that loop in virtqueue_poll() till new buffers become available? > accordingly, virtio_queue_set_notification_and_check > will accept this opaque value and check avail buffers > against it. Can you show me the pseudo-code? Thanks Michael On 2024/7/2, 19:27, "Michael S. Tsirkin" <mst@redhat.com <mailto:mst@redhat.com>> wrote: On Tue, Jul 02, 2024 at 07:45:31AM +0800, Yang Dongshan wrote: > > what does "changed" mean here? changed compared to what? > For a split queue, if the shadow_avail_idx synced from avail ring idx > by vring_avail_idx(vq) last time doesn't equal the current value of avail ring > idx. > > vq->shadow_avail_idx != vring_avail_idx(vq); > > For packed queue, the logic is similar, if vq->shadow_avail_idx > > becomes available, it means the guest has added buf at the slot. > > vring_packed_desc_read(vq->vdev, &desc, &caches->desc, > > vq->shadow_avail_idx, true); > > if (is_desc_avail(desc.flags, vq-> shadow_avail_wrap_counter)) > > return true; > > My suggestion: change virtqueue_get_avail_bytes to return the shadow in an opaque unsigned value. add virtqueue_poll that gets this opaque and tells us whether any new buffers became available in the queue since that value was returned. accordingly, virtio_queue_set_notification_and_check will accept this opaque value and check avail buffers against it. > On Tue, Jul 2, 2024 at 2:46 AM Michael S. Tsirkin <mst@redhat.com <mailto:mst@redhat.com>> wrote: > > On Tue, Jul 02, 2024 at 01:18:15AM +0800, Yang Dongshan wrote: > > > Please document what this does. > > okay, i will. > > > > > So this will return false if ring has any available buffers? > > > Equivalent to: > > > > > > bool virtio_queue_set_notification_and_check(VirtQueue *vq, int enable) > > > { > > > virtio_queue_packed_set_notification(vq, enable); > > > return virtio_queue_empty(vq); > > > } > > > > No, only when the shadow_avail_idx is changed shall the function return > true, > > > what does "changed" mean here? changed compared to what? > > > compared with the value seen by the host last time, else return false > even if > > there are some buffers available in the queue, as the total size of the > > available > > buffers in the queue can't satisfy the request. > > > > It maybe better to pass only one arg to the function like this: > > bool virtio_queue_set_notification_and_check(VirtQueue *vq) > > { > > virtio_queue_packed_set_notification(vq, true); > > > > return shadow_avail_idx_changed()? true: false; > > } > > > > Thanks Michael a lot! > > > > On Mon, Jul 1, 2024 at 11:05 PM Michael S. Tsirkin <mst@redhat.com <mailto:mst@redhat.com>> > wrote: > > > > On Mon, Jul 01, 2024 at 10:00:17PM +0800, Wencheng Yang wrote: > > > From: thomas <east.moutain.yang@gmail.com <mailto:east.moutain.yang@gmail.com>> > > > > > > Patch 06b12970174 ("virtio-net: fix network stall under load") > > > added double-check to test whether the available buffer size > > > can satisfy the request or not, in case the guest has added > > > some buffers to the avail ring simultaneously after the first > > > check. It will be lucky if the available buffer size becomes > > > okay after the double-check, then the host can send the packet > > > to the guest. If the buffer size still can't satisfy the request, > > > even if the guest has added some buffers, viritio-net would > > > stall at the host side forever. > > > > > > The patch checks whether the guest has added some buffers > > > after last check of avail idx when the available buffers are > > > not sufficient, if so then recheck the available buffers > > > in the loop. > > > > > > The patch also reverts patch "06b12970174". > > > > > > The case below can reproduce the stall. > > > > > > Guest 0 > > > +--------+ > > > | iperf | > > > ---------------> | server | > > > Host | +--------+ > > > +--------+ | ... > > > | iperf |---- > > > | client |---- Guest n > > > +--------+ | +--------+ > > > | | iperf | > > > ---------------> | server | > > > +--------+ > > > > > > Boot many guests from qemu with virtio network: > > > qemu ... -netdev tap,id=net_x \ > > > -device virtio-net-pci-non-transitional,\ > > > iommu_platform=on,mac=xx:xx:xx:xx:xx:xx,netdev=net_x > > > > > > Each guest acts as iperf server with commands below: > > > iperf3 -s -D -i 10 -p 8001 > > > iperf3 -s -D -i 10 -p 8002 > > > > > > The host as iperf client: > > > iperf3 -c guest_IP -p 8001 -i 30 -w 256k -P 20 -t 40000 > > > iperf3 -c guest_IP -p 8002 -i 30 -w 256k -P 20 -t 40000 > > > > > > After some time, the host loses connection to the guest, > > > the guest can send packet to the host, but can't receive > > > packet from host. > > > > > > It's more likely to happen if SWIOTLB is enabled in the guest, > > > allocating and freeing bounce buffer takes some CPU ticks, > > > copying from/to bounce buffer takes more CPU ticks, compared > > > with that there is no bounce buffer in the guest. > > > Once the rate of producing packets from the host approximates > > > the rate of receiveing packets in the guest, the guest would > > > loop in NAPI. > > > > > > receive packets --- > > > | | > > > v | > > > free buf virtnet_poll > > > | | > > > v | > > > add buf to avail ring --- > > > | > > > | need kick the host? > > > | NAPI continues > > > v > > > receive packets --- > > > | | > > > v | > > > free buf virtnet_poll > > > | | > > > v | > > > add buf to avail ring --- > > > | > > > v > > > ... ... > > > > > > On the other hand, the host fetches free buf from avail > > > ring, if the buf in the avail ring is not enough, the > > > host notifies the guest the event by writing the avail > > > idx read from avail ring to the event idx of used ring, > > > then the host goes to sleep, waiting for the kick signal > > > from the guest. > > > > > > Once the guest finds the host is waiting for kick singal > > > (in virtqueue_kick_prepare_split()), it kicks the host. > > > > > > The host may stall forever at the sequences below: > > > > > > Host Guest > > > ------------ ----------- > > > fetch buf, send packet receive packet --- > > > ... ... | > > > fetch buf, send packet add buf | > > > ... add buf virtnet_poll > > > buf not enough avail idx-> add buf | > > > read avail idx add buf | > > > add buf --- > > > receive packet --- > > > write event idx ... | > > > wait for kick add buf virtnet_poll > > > ... | > > > --- > > > no more packet, exit NAPI > > > > > > In the first loop of NAPI above, indicated in the range of > > > virtnet_poll above, the host is sending packets while the > > > guest is receiving packets and adding buffers. > > > step 1: The buf is not enough, for example, a big packet > > > needs 5 buf, but the available buf count is 3. > > > The host read current avail idx. > > > step 2: The guest adds some buf, then checks whether the > > > host is waiting for kick signal, not at this time. > > > The used ring is not empty, the guest continues > > > the second loop of NAPI. > > > step 3: The host writes the avail idx read from avail > > > ring to used ring as event idx via > > > virtio_queue_set_notification(q->rx_vq, 1). > > > step 4: At the end of the second loop of NAPI, recheck > > > whether kick is needed, as the event idx in the > > > used ring written by the host is beyound the > > > range of kick condition, the guest will not > > > send kick signal to the host. > > > > > > Fixes: 06b12970174 ("virtio-net: fix network stall under load") > > > Signed-off-by: Wencheng Yang <east.moutain.yang@gmail.com <mailto:east.moutain.yang@gmail.com>> > > > --- > > > > > > Changelog: > > > v7: > > > - Add function virtio_queue_set_notification_and_check() > > > - Restore the function sequence introduce in v6 > > > > > > v6: > > > - Take packed packed queue into cosideration > > > - Adjust function sequence to fix compilation issue > > > > > > v5: > > > - Modify return type of virtio_queue_set_notification() to > > > bool to indicate whether the guest has added some buffers > > > after last check of avail idx > > > - Loop in virtio_net_has_buffers() if the available buffers > > > are not sufficient and the guest has added some buffers. > > > - Revert patch "06b12970174" > > > - Update the subject > > > > > > v4: > > > - Correct spelling mistake in the subject > > > - Describe the issue that virtio-net is blocked at host side > > > > > > v3: > > > - Add virtio-net tag in the subject > > > - Refine commit log > > > > > > v2: > > > - Add SOB tag at the end of the commit message > > > - Place Fixes tag at the end of the commit message > > > > > > v1: > > > - Initial patch > > > > > > hw/net/virtio-net.c | 19 ++++++++----------- > > > hw/virtio/virtio.c | 39 > ++++++++++++++++++++++++++++++++++++++ > > > include/hw/virtio/virtio.h | 1 + > > > 3 files changed, 48 insertions(+), 11 deletions(-) > > > > > > diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c > > > index 9c7e85caea..357c651d9b 100644 > > > --- a/hw/net/virtio-net.c > > > +++ b/hw/net/virtio-net.c > > > @@ -1642,18 +1642,15 @@ static bool virtio_net_can_receive > (NetClientState > > *nc) > > > static int virtio_net_has_buffers(VirtIONetQueue *q, int bufsize) > > > { > > > VirtIONet *n = q->n; > > > - if (virtio_queue_empty(q->rx_vq) || > > > - (n->mergeable_rx_bufs && > > > - !virtqueue_avail_bytes(q->rx_vq, bufsize, 0))) { > > > - virtio_queue_set_notification(q->rx_vq, 1); > > > - > > > - /* To avoid a race condition where the guest has made some > > buffers > > > - * available after the above check but before notification > was > > > - * enabled, check for available buffers again. > > > - */ > > > - if (virtio_queue_empty(q->rx_vq) || > > > + > > > + while (virtio_queue_empty(q->rx_vq) || > > > (n->mergeable_rx_bufs && > > > - !virtqueue_avail_bytes(q->rx_vq, bufsize, 0))) { > > > + !virtqueue_avail_bytes(q->rx_vq, bufsize, 0))) { > > > + /* guest may have made some buf, try again */ > > > + if (virtio_queue_set_notification_and_check(q->rx_vq, 1)) > { > > > + virtio_queue_set_notification(q->rx_vq, 0); > > > + continue; > > > + } else { > > > return 0; > > > } > > > } > > > diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c > > > index 893a072c9d..b165764017 100644 > > > --- a/hw/virtio/virtio.c > > > +++ b/hw/virtio/virtio.c > > > @@ -668,6 +668,45 @@ static inline bool is_desc_avail(uint16_t > flags, > > bool wrap_counter) > > > return (avail != used) && (avail == wrap_counter); > > > } > > > > > > +bool virtio_queue_set_notification_and_check(VirtQueue *vq, int > enable) > > > +{ > > > + uint16_t shadow_idx; > > > + VRingPackedDesc desc; > > > + VRingMemoryRegionCaches *caches; > > > + > > > + vq->notification = enable; > > > + > > > + if (!vq->vring.desc) { > > > + return false; > > > + } > > > + > > > + if (virtio_vdev_has_feature(vq->vdev, VIRTIO_F_RING_PACKED)) { > > > + virtio_queue_packed_set_notification(vq, enable); > > > + > > > + if (enable) { > > > + caches = vring_get_region_caches(vq); > > > + if (!caches) { > > > + return false; > > > + } > > > + > > > + vring_packed_desc_read(vq->vdev, &desc, &caches->desc, > > > + vq->shadow_avail_idx, true); > > > + if (is_desc_avail(desc.flags, vq-> > > shadow_avail_wrap_counter)) { > > > + return true; > > > + } > > > + } > > > + } else { > > > + shadow_idx = vq->shadow_avail_idx; > > > + virtio_queue_split_set_notification(vq, enable); > > > + > > > + if (enable) { > > > + return shadow_idx != vring_avail_idx(vq); > > > + } > > > + } > > > + > > > + return false; > > > +} > > > > Please document what this does. > > So this will return false if ring has any availabe buffers? > > Equivalent to: > > > > bool virtio_queue_set_notification_and_check(VirtQueue *vq, int > enable) > > { > > virtio_queue_packed_set_notification(vq, enable); > > return virtio_queue_empty(vq); > > } > > > > > > or am I missing something? > > > > > + > > > /* Fetch avail_idx from VQ memory only when we really need to know > if > > > * guest has added some buffers. > > > * Called within rcu_read_lock(). */ > > > diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/ > virtio.h > > > index 7d5ffdc145..ed85023b87 100644 > > > --- a/include/hw/virtio/virtio.h > > > +++ b/include/hw/virtio/virtio.h > > > @@ -302,6 +302,7 @@ void virtio_notify_config(VirtIODevice *vdev); > > > > > > bool virtio_queue_get_notification(VirtQueue *vq); > > > void virtio_queue_set_notification(VirtQueue *vq, int enable); > > > +bool virtio_queue_set_notification_and_check(VirtQueue *vq, int > enable); > > > > > > int virtio_queue_ready(VirtQueue *vq); > > > > > > -- > > > 2.39.0 > > > > > >
diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c index 9c7e85caea..357c651d9b 100644 --- a/hw/net/virtio-net.c +++ b/hw/net/virtio-net.c @@ -1642,18 +1642,15 @@ static bool virtio_net_can_receive(NetClientState *nc) static int virtio_net_has_buffers(VirtIONetQueue *q, int bufsize) { VirtIONet *n = q->n; - if (virtio_queue_empty(q->rx_vq) || - (n->mergeable_rx_bufs && - !virtqueue_avail_bytes(q->rx_vq, bufsize, 0))) { - virtio_queue_set_notification(q->rx_vq, 1); - - /* To avoid a race condition where the guest has made some buffers - * available after the above check but before notification was - * enabled, check for available buffers again. - */ - if (virtio_queue_empty(q->rx_vq) || + + while (virtio_queue_empty(q->rx_vq) || (n->mergeable_rx_bufs && - !virtqueue_avail_bytes(q->rx_vq, bufsize, 0))) { + !virtqueue_avail_bytes(q->rx_vq, bufsize, 0))) { + /* guest may have made some buf, try again */ + if (virtio_queue_set_notification_and_check(q->rx_vq, 1)) { + virtio_queue_set_notification(q->rx_vq, 0); + continue; + } else { return 0; } } diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c index 893a072c9d..b165764017 100644 --- a/hw/virtio/virtio.c +++ b/hw/virtio/virtio.c @@ -668,6 +668,45 @@ static inline bool is_desc_avail(uint16_t flags, bool wrap_counter) return (avail != used) && (avail == wrap_counter); } +bool virtio_queue_set_notification_and_check(VirtQueue *vq, int enable) +{ + uint16_t shadow_idx; + VRingPackedDesc desc; + VRingMemoryRegionCaches *caches; + + vq->notification = enable; + + if (!vq->vring.desc) { + return false; + } + + if (virtio_vdev_has_feature(vq->vdev, VIRTIO_F_RING_PACKED)) { + virtio_queue_packed_set_notification(vq, enable); + + if (enable) { + caches = vring_get_region_caches(vq); + if (!caches) { + return false; + } + + vring_packed_desc_read(vq->vdev, &desc, &caches->desc, + vq->shadow_avail_idx, true); + if (is_desc_avail(desc.flags, vq->shadow_avail_wrap_counter)) { + return true; + } + } + } else { + shadow_idx = vq->shadow_avail_idx; + virtio_queue_split_set_notification(vq, enable); + + if (enable) { + return shadow_idx != vring_avail_idx(vq); + } + } + + return false; +} + /* Fetch avail_idx from VQ memory only when we really need to know if * guest has added some buffers. * Called within rcu_read_lock(). */ diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h index 7d5ffdc145..ed85023b87 100644 --- a/include/hw/virtio/virtio.h +++ b/include/hw/virtio/virtio.h @@ -302,6 +302,7 @@ void virtio_notify_config(VirtIODevice *vdev); bool virtio_queue_get_notification(VirtQueue *vq); void virtio_queue_set_notification(VirtQueue *vq, int enable); +bool virtio_queue_set_notification_and_check(VirtQueue *vq, int enable); int virtio_queue_ready(VirtQueue *vq);