| Message ID | 530DB1C9.2060106@huawei.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 2014/2/26 17:20, Qin Chuanyu wrote: > guest kick host base on avail_ring flags value and get perfermance > improved, vhost_zerocopy_callback could do the same thing. As > virtqueue_enable_cb need one more check after modifying the value of > avail_ring flags, vhost also need do the same thing after > vhost_enable_notify. > > test result list as below: > guest and host: suse11sp3, netperf, intel CPU 2.4GHz > +------+----------+--------+----------+--------+--------+---------+ > | | old | new | > +------+----------+--------+----------+--------+--------+---------+ > | UDP | Gbit/s | PPS |CPU idle% | Gbit/s | PPS |CPU idle%| > | 256 | 0.74805 | 321309 | 87.16 | 0.77933| 334743 | 90.71 | > | 512 | 1.42 | 328475 | 87.03 | 1.44 | 333550 | 90.43 | > | 1024 | 2.79 | 334426 | 89.09 | 2.81 | 336986 | 89.55 | > | 1460 | 3.71 | 316215 | 87.53 | 4.02 | 342325 | 89.58 | > +------+----------+--------+----------+--------+--------+---------+ > > Signed-off-by: Chuanyu Qin <qinchuanyu@huawei.com> > --- > drivers/vhost/net.c | 13 ++++++++++++- > 1 files changed, 12 insertions(+), 1 deletions(-) > > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c > index a0fa5de..a90f51b 100644 > --- a/drivers/vhost/net.c > +++ b/drivers/vhost/net.c > @@ -315,6 +315,10 @@ static void vhost_zerocopy_callback(struct ubuf_info *ubuf, bool success) > VHOST_DMA_DONE_LEN : VHOST_DMA_FAILED_LEN; > cnt = vhost_net_ubuf_put(ubufs); > > + /* make sure len has been updated because handle_tx would use it > + * and used_flags should also been checked. > + */ > + smp_mb(); > /* > * Trigger polling thread if guest stopped submitting new buffers: > * in this case, the refcount after decrement will eventually reach 1. > @@ -322,7 +326,8 @@ static void vhost_zerocopy_callback(struct ubuf_info *ubuf, bool success) > * (the value 16 here is more or less arbitrary, it's tuned to trigger > * less than 10% of times). > */ > - if (cnt <= 1 || !(cnt % 16)) > + if ((!(vq->used_flags & VRING_USED_F_NO_NOTIFY)) > + && (cnt <= 1 || !(cnt % 16))) > vhost_poll_queue(&vq->poll); > > rcu_read_unlock_bh(); > @@ -386,6 +391,12 @@ static void handle_tx(struct vhost_net *net) > vhost_disable_notify(&net->dev, vq); > continue; > } > + /* there might skb been freed between last Not aligned here. -Ding > + * vhost_zerocopy_signal_used and vhost_enable_notify, > + * so one more check is needed. > + */ > + if (zcopy) > + vhost_zerocopy_signal_used(net, vq); > break; > } > if (in) { -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Please see MAINTAINERS and copy all relevant lists. On Wed, Feb 26, 2014 at 05:20:09PM +0800, Qin Chuanyu wrote: > guest kick host base on avail_ring flags value and get perfermance typo > improved, vhost_zerocopy_callback could do the same thing. As > virtqueue_enable_cb need one more check after modifying the value of > avail_ring flags, vhost also need do the same thing after > vhost_enable_notify. > > test result list as below: > guest and host: suse11sp3, netperf, intel CPU 2.4GHz > +------+----------+--------+----------+--------+--------+---------+ > | | old | new | > +------+----------+--------+----------+--------+--------+---------+ > | UDP | Gbit/s | PPS |CPU idle% | Gbit/s | PPS |CPU idle%| > | 256 | 0.74805 | 321309 | 87.16 | 0.77933| 334743 | 90.71 | > | 512 | 1.42 | 328475 | 87.03 | 1.44 | 333550 | 90.43 | > | 1024 | 2.79 | 334426 | 89.09 | 2.81 | 336986 | 89.55 | > | 1460 | 3.71 | 316215 | 87.53 | 4.02 | 342325 | 89.58 | > +------+----------+--------+----------+--------+--------+---------+ > > Signed-off-by: Chuanyu Qin <qinchuanyu@huawei.com> It's an interesting optimization, thanks! However, it looks like this might delay updating used ring indefinitely if we are unlucky. Some guests (e.g. windows) tend to crash if this happens. Maybe use a new flag for this? It also looks like there are potential race conditions below. > --- > drivers/vhost/net.c | 13 ++++++++++++- > 1 files changed, 12 insertions(+), 1 deletions(-) > > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c > index a0fa5de..a90f51b 100644 > --- a/drivers/vhost/net.c > +++ b/drivers/vhost/net.c > @@ -315,6 +315,10 @@ static void vhost_zerocopy_callback(struct > ubuf_info *ubuf, bool success) > VHOST_DMA_DONE_LEN : VHOST_DMA_FAILED_LEN; > cnt = vhost_net_ubuf_put(ubufs); > > + /* make sure len has been updated because handle_tx would use it > + * and used_flags should also been checked. > + */ > + smp_mb(); > /* > * Trigger polling thread if guest stopped submitting new buffers: > * in this case, the refcount after decrement will eventually reach 1. this barrier is very suspect. > @@ -322,7 +326,8 @@ static void vhost_zerocopy_callback(struct > ubuf_info *ubuf, bool success) > * (the value 16 here is more or less arbitrary, it's tuned to trigger > * less than 10% of times). > */ > - if (cnt <= 1 || !(cnt % 16)) > + if ((!(vq->used_flags & VRING_USED_F_NO_NOTIFY)) > + && (cnt <= 1 || !(cnt % 16))) > vhost_poll_queue(&vq->poll); > > rcu_read_unlock_bh(); looks like a potential race to me > @@ -386,6 +391,12 @@ static void handle_tx(struct vhost_net *net) > vhost_disable_notify(&net->dev, vq); > continue; > } > + /* there might skb been freed between last > + * vhost_zerocopy_signal_used and vhost_enable_notify, > + * so one more check is needed. > + */ > + if (zcopy) > + vhost_zerocopy_signal_used(net, vq); > break; > } > if (in) { > -- > 1.7.3.1.msysgit.0 > -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 02/26/2014 07:16 PM, Michael S. Tsirkin wrote: > Please see MAINTAINERS and copy all relevant lists. > > On Wed, Feb 26, 2014 at 05:20:09PM +0800, Qin Chuanyu wrote: >> guest kick host base on avail_ring flags value and get perfermance > typo > >> improved, vhost_zerocopy_callback could do the same thing. As >> virtqueue_enable_cb need one more check after modifying the value of >> avail_ring flags, vhost also need do the same thing after >> vhost_enable_notify. >> >> test result list as below: >> guest and host: suse11sp3, netperf, intel CPU 2.4GHz >> +------+----------+--------+----------+--------+--------+---------+ >> | | old | new | >> +------+----------+--------+----------+--------+--------+---------+ >> | UDP | Gbit/s | PPS |CPU idle% | Gbit/s | PPS |CPU idle%| >> | 256 | 0.74805 | 321309 | 87.16 | 0.77933| 334743 | 90.71 | >> | 512 | 1.42 | 328475 | 87.03 | 1.44 | 333550 | 90.43 | >> | 1024 | 2.79 | 334426 | 89.09 | 2.81 | 336986 | 89.55 | >> | 1460 | 3.71 | 316215 | 87.53 | 4.02 | 342325 | 89.58 | >> +------+----------+--------+----------+--------+--------+---------+ >> >> Signed-off-by: Chuanyu Qin <qinchuanyu@huawei.com> > It's an interesting optimization, thanks! > However, it looks like this might delay > updating used ring indefinitely if we are > unlucky. Some guests (e.g. windows) > tend to crash if this happens. Looks like it does not change this. When tx notification is disabled, it means handle_tx() is running which will update the used ring before each tx descriptor fetching. And the patch does used updating after each time when tx notification is enabled. > > Maybe use a new flag for this? > > It also looks like there are potential race conditions below. > >> --- >> drivers/vhost/net.c | 13 ++++++++++++- >> 1 files changed, 12 insertions(+), 1 deletions(-) >> >> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c >> index a0fa5de..a90f51b 100644 >> --- a/drivers/vhost/net.c >> +++ b/drivers/vhost/net.c >> @@ -315,6 +315,10 @@ static void vhost_zerocopy_callback(struct >> ubuf_info *ubuf, bool success) >> VHOST_DMA_DONE_LEN : VHOST_DMA_FAILED_LEN; >> cnt = vhost_net_ubuf_put(ubufs); >> >> + /* make sure len has been updated because handle_tx would use it >> + * and used_flags should also been checked. >> + */ >> + smp_mb(); >> /* >> * Trigger polling thread if guest stopped submitting new buffers: >> * in this case, the refcount after decrement will eventually reach 1. > this barrier is very suspect. > >> @@ -322,7 +326,8 @@ static void vhost_zerocopy_callback(struct >> ubuf_info *ubuf, bool success) >> * (the value 16 here is more or less arbitrary, it's tuned to trigger >> * less than 10% of times). >> */ >> - if (cnt <= 1 || !(cnt % 16)) >> + if ((!(vq->used_flags & VRING_USED_F_NO_NOTIFY)) >> + && (cnt <= 1 || !(cnt % 16))) >> vhost_poll_queue(&vq->poll); >> >> rcu_read_unlock_bh(); > looks like a potential race to me Could you please explain the race a little bit more? >> @@ -386,6 +391,12 @@ static void handle_tx(struct vhost_net *net) >> vhost_disable_notify(&net->dev, vq); >> continue; >> } >> + /* there might skb been freed between last >> + * vhost_zerocopy_signal_used and vhost_enable_notify, >> + * so one more check is needed. >> + */ >> + if (zcopy) >> + vhost_zerocopy_signal_used(net, vq); > >> break; >> } >> if (in) { >> -- >> 1.7.3.1.msysgit.0 >> > -- > To unsubscribe from this list: send the line "unsubscribe kvm" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c index a0fa5de..a90f51b 100644 --- a/drivers/vhost/net.c +++ b/drivers/vhost/net.c @@ -315,6 +315,10 @@ static void vhost_zerocopy_callback(struct ubuf_info *ubuf, bool success) VHOST_DMA_DONE_LEN : VHOST_DMA_FAILED_LEN; cnt = vhost_net_ubuf_put(ubufs); + /* make sure len has been updated because handle_tx would use it + * and used_flags should also been checked. + */ + smp_mb(); /* * Trigger polling thread if guest stopped submitting new buffers:
guest kick host base on avail_ring flags value and get perfermance improved, vhost_zerocopy_callback could do the same thing. As virtqueue_enable_cb need one more check after modifying the value of avail_ring flags, vhost also need do the same thing after vhost_enable_notify. test result list as below: guest and host: suse11sp3, netperf, intel CPU 2.4GHz +------+----------+--------+----------+--------+--------+---------+ | | old | new | +------+----------+--------+----------+--------+--------+---------+ | UDP | Gbit/s | PPS |CPU idle% | Gbit/s | PPS |CPU idle%| | 256 | 0.74805 | 321309 | 87.16 | 0.77933| 334743 | 90.71 | | 512 | 1.42 | 328475 | 87.03 | 1.44 | 333550 | 90.43 | | 1024 | 2.79 | 334426 | 89.09 | 2.81 | 336986 | 89.55 | | 1460 | 3.71 | 316215 | 87.53 | 4.02 | 342325 | 89.58 | +------+----------+--------+----------+--------+--------+---------+ Signed-off-by: Chuanyu Qin <qinchuanyu@huawei.com> --- drivers/vhost/net.c | 13 ++++++++++++- 1 files changed, 12 insertions(+), 1 deletions(-) * in this case, the refcount after decrement will eventually reach 1. @@ -322,7 +326,8 @@ static void vhost_zerocopy_callback(struct ubuf_info *ubuf, bool success) * (the value 16 here is more or less arbitrary, it's tuned to trigger * less than 10% of times). */ - if (cnt <= 1 || !(cnt % 16)) + if ((!(vq->used_flags & VRING_USED_F_NO_NOTIFY)) + && (cnt <= 1 || !(cnt % 16))) vhost_poll_queue(&vq->poll); rcu_read_unlock_bh(); @@ -386,6 +391,12 @@ static void handle_tx(struct vhost_net *net) vhost_disable_notify(&net->dev, vq); continue; } + /* there might skb been freed between last + * vhost_zerocopy_signal_used and vhost_enable_notify, + * so one more check is needed. + */ + if (zcopy) + vhost_zerocopy_signal_used(net, vq); break; } if (in) {