| Message ID | 20200212072635.682689-5-leon@kernel.org (mailing list archive) |
|---|---|
| State | Changes Requested |
| Headers | show |
| Series | Fixes for v5.6 | expand |
On Wed, Feb 12, 2020 at 09:26:30AM +0200, Leon Romanovsky wrote: > diff --git a/drivers/infiniband/ulp/ipoib/ipoib.h b/drivers/infiniband/ulp/ipoib/ipoib.h > index 2aa3457a30ce..c614cb87d09b 100644 > --- a/drivers/infiniband/ulp/ipoib/ipoib.h > +++ b/drivers/infiniband/ulp/ipoib/ipoib.h > @@ -379,6 +379,7 @@ struct ipoib_dev_priv { > struct ipoib_tx_buf *tx_ring; > unsigned int tx_head; > unsigned int tx_tail; > + atomic_t tx_outstanding; > struct ib_sge tx_sge[MAX_SKB_FRAGS + 1]; > struct ib_ud_wr tx_wr; > struct ib_wc send_wc[MAX_SEND_CQE]; > diff --git a/drivers/infiniband/ulp/ipoib/ipoib_cm.c b/drivers/infiniband/ulp/ipoib/ipoib_cm.c > index c59e00a0881f..db6aace83fe5 100644 > --- a/drivers/infiniband/ulp/ipoib/ipoib_cm.c > +++ b/drivers/infiniband/ulp/ipoib/ipoib_cm.c > @@ -756,7 +756,7 @@ void ipoib_cm_send(struct net_device *dev, struct sk_buff *skb, struct ipoib_cm_ > return; > } > > - if ((priv->tx_head - priv->tx_tail) == ipoib_sendq_size - 1) { > + if (atomic_read(&priv->tx_outstanding) == ipoib_sendq_size - 1) { > ipoib_dbg(priv, "TX ring 0x%x full, stopping kernel net queue\n", > tx->qp->qp_num); > netif_stop_queue(dev); > @@ -786,7 +786,7 @@ void ipoib_cm_send(struct net_device *dev, struct sk_buff *skb, struct ipoib_cm_ > } else { > netif_trans_update(dev); > ++tx->tx_head; > - ++priv->tx_head; > + atomic_inc(&priv->tx_outstanding); > } This use of an atomic is very weird, probably wrong. Why is it an atomic? priv->tx_head wasn't an atomic, and every place touching tx_outstanding was also touching tx_head. I assume there is some hidden locking here? Or much more stuff is busted up. In that case, drop the atomic. However, if the atomic is needed (where/why?) then something has to be dealing with the races, and if the write side is fully locked then an atomic is the wrong choice, use READ_ONCE/WRITE_ONCE instead Jason
On Thu, Feb 13, 2020 at 11:37:43AM -0400, Jason Gunthorpe wrote: > On Wed, Feb 12, 2020 at 09:26:30AM +0200, Leon Romanovsky wrote: > > > diff --git a/drivers/infiniband/ulp/ipoib/ipoib.h b/drivers/infiniband/ulp/ipoib/ipoib.h > > index 2aa3457a30ce..c614cb87d09b 100644 > > --- a/drivers/infiniband/ulp/ipoib/ipoib.h > > +++ b/drivers/infiniband/ulp/ipoib/ipoib.h > > @@ -379,6 +379,7 @@ struct ipoib_dev_priv { > > struct ipoib_tx_buf *tx_ring; > > unsigned int tx_head; > > unsigned int tx_tail; > > + atomic_t tx_outstanding; > > struct ib_sge tx_sge[MAX_SKB_FRAGS + 1]; > > struct ib_ud_wr tx_wr; > > struct ib_wc send_wc[MAX_SEND_CQE]; > > diff --git a/drivers/infiniband/ulp/ipoib/ipoib_cm.c b/drivers/infiniband/ulp/ipoib/ipoib_cm.c > > index c59e00a0881f..db6aace83fe5 100644 > > --- a/drivers/infiniband/ulp/ipoib/ipoib_cm.c > > +++ b/drivers/infiniband/ulp/ipoib/ipoib_cm.c > > @@ -756,7 +756,7 @@ void ipoib_cm_send(struct net_device *dev, struct sk_buff *skb, struct ipoib_cm_ > > return; > > } > > > > - if ((priv->tx_head - priv->tx_tail) == ipoib_sendq_size - 1) { > > + if (atomic_read(&priv->tx_outstanding) == ipoib_sendq_size - 1) { > > ipoib_dbg(priv, "TX ring 0x%x full, stopping kernel net queue\n", > > tx->qp->qp_num); > > netif_stop_queue(dev); > > @@ -786,7 +786,7 @@ void ipoib_cm_send(struct net_device *dev, struct sk_buff *skb, struct ipoib_cm_ > > } else { > > netif_trans_update(dev); > > ++tx->tx_head; > > - ++priv->tx_head; > > + atomic_inc(&priv->tx_outstanding); > > } > > This use of an atomic is very weird, probably wrong. > > Why is it an atomic? priv->tx_head wasn't an atomic, and every place > touching tx_outstanding was also touching tx_head. > > I assume there is some hidden locking here? Or much more stuff is > busted up. > > In that case, drop the atomic. > > However, if the atomic is needed (where/why?) then something has to > be dealing with the races, and if the write side is fully locked then > an atomic is the wrong choice, use READ_ONCE/WRITE_ONCE instead I thought that atomic_t is appropriate here. Valentin wanted to implement "window" and he needed to ensure that this window is counted correctly while it doesn't need to be 100% accurate. Thanks > > Jason
On Thu, Feb 13, 2020 at 08:10:12PM +0200, Leon Romanovsky wrote: > On Thu, Feb 13, 2020 at 11:37:43AM -0400, Jason Gunthorpe wrote: > > On Wed, Feb 12, 2020 at 09:26:30AM +0200, Leon Romanovsky wrote: > > > > > diff --git a/drivers/infiniband/ulp/ipoib/ipoib.h b/drivers/infiniband/ulp/ipoib/ipoib.h > > > index 2aa3457a30ce..c614cb87d09b 100644 > > > +++ b/drivers/infiniband/ulp/ipoib/ipoib.h > > > @@ -379,6 +379,7 @@ struct ipoib_dev_priv { > > > struct ipoib_tx_buf *tx_ring; > > > unsigned int tx_head; > > > unsigned int tx_tail; > > > + atomic_t tx_outstanding; > > > struct ib_sge tx_sge[MAX_SKB_FRAGS + 1]; > > > struct ib_ud_wr tx_wr; > > > struct ib_wc send_wc[MAX_SEND_CQE]; > > > diff --git a/drivers/infiniband/ulp/ipoib/ipoib_cm.c b/drivers/infiniband/ulp/ipoib/ipoib_cm.c > > > index c59e00a0881f..db6aace83fe5 100644 > > > +++ b/drivers/infiniband/ulp/ipoib/ipoib_cm.c > > > @@ -756,7 +756,7 @@ void ipoib_cm_send(struct net_device *dev, struct sk_buff *skb, struct ipoib_cm_ > > > return; > > > } > > > > > > - if ((priv->tx_head - priv->tx_tail) == ipoib_sendq_size - 1) { > > > + if (atomic_read(&priv->tx_outstanding) == ipoib_sendq_size - 1) { > > > ipoib_dbg(priv, "TX ring 0x%x full, stopping kernel net queue\n", > > > tx->qp->qp_num); > > > netif_stop_queue(dev); > > > @@ -786,7 +786,7 @@ void ipoib_cm_send(struct net_device *dev, struct sk_buff *skb, struct ipoib_cm_ > > > } else { > > > netif_trans_update(dev); > > > ++tx->tx_head; > > > - ++priv->tx_head; > > > + atomic_inc(&priv->tx_outstanding); > > > } > > > > This use of an atomic is very weird, probably wrong. > > > > Why is it an atomic? priv->tx_head wasn't an atomic, and every place > > touching tx_outstanding was also touching tx_head. > > > > I assume there is some hidden locking here? Or much more stuff is > > busted up. > > > > In that case, drop the atomic. > > > > However, if the atomic is needed (where/why?) then something has to > > be dealing with the races, and if the write side is fully locked then > > an atomic is the wrong choice, use READ_ONCE/WRITE_ONCE instead > > I thought that atomic_t is appropriate here. Valentin wanted to > implement "window" and he needed to ensure that this window is counted > correctly while it doesn't need to be 100% accurate. It does need to be 100% accurate because the stop_queue condition is: + if (atomic_read(&priv->tx_outstanding) == ipoib_sendq_size - 1) { And presumably the whole problem here is overflowing some sized q opbject. That atomic is only needed if there is concurrency, and where is the concurrency? Jason
On Thu, Feb 13, 2020 at 02:26:55PM -0400, Jason Gunthorpe wrote: > On Thu, Feb 13, 2020 at 08:10:12PM +0200, Leon Romanovsky wrote: > > On Thu, Feb 13, 2020 at 11:37:43AM -0400, Jason Gunthorpe wrote: > > > On Wed, Feb 12, 2020 at 09:26:30AM +0200, Leon Romanovsky wrote: > > > > > > > diff --git a/drivers/infiniband/ulp/ipoib/ipoib.h b/drivers/infiniband/ulp/ipoib/ipoib.h > > > > index 2aa3457a30ce..c614cb87d09b 100644 > > > > +++ b/drivers/infiniband/ulp/ipoib/ipoib.h > > > > @@ -379,6 +379,7 @@ struct ipoib_dev_priv { > > > > struct ipoib_tx_buf *tx_ring; > > > > unsigned int tx_head; > > > > unsigned int tx_tail; > > > > + atomic_t tx_outstanding; > > > > struct ib_sge tx_sge[MAX_SKB_FRAGS + 1]; > > > > struct ib_ud_wr tx_wr; > > > > struct ib_wc send_wc[MAX_SEND_CQE]; > > > > diff --git a/drivers/infiniband/ulp/ipoib/ipoib_cm.c b/drivers/infiniband/ulp/ipoib/ipoib_cm.c > > > > index c59e00a0881f..db6aace83fe5 100644 > > > > +++ b/drivers/infiniband/ulp/ipoib/ipoib_cm.c > > > > @@ -756,7 +756,7 @@ void ipoib_cm_send(struct net_device *dev, struct sk_buff *skb, struct ipoib_cm_ > > > > return; > > > > } > > > > > > > > - if ((priv->tx_head - priv->tx_tail) == ipoib_sendq_size - 1) { > > > > + if (atomic_read(&priv->tx_outstanding) == ipoib_sendq_size - 1) { > > > > ipoib_dbg(priv, "TX ring 0x%x full, stopping kernel net queue\n", > > > > tx->qp->qp_num); > > > > netif_stop_queue(dev); > > > > @@ -786,7 +786,7 @@ void ipoib_cm_send(struct net_device *dev, struct sk_buff *skb, struct ipoib_cm_ > > > > } else { > > > > netif_trans_update(dev); > > > > ++tx->tx_head; > > > > - ++priv->tx_head; > > > > + atomic_inc(&priv->tx_outstanding); > > > > } > > > > > > This use of an atomic is very weird, probably wrong. > > > > > > Why is it an atomic? priv->tx_head wasn't an atomic, and every place > > > touching tx_outstanding was also touching tx_head. > > > > > > I assume there is some hidden locking here? Or much more stuff is > > > busted up. > > > > > > In that case, drop the atomic. > > > > > > However, if the atomic is needed (where/why?) then something has to > > > be dealing with the races, and if the write side is fully locked then > > > an atomic is the wrong choice, use READ_ONCE/WRITE_ONCE instead > > > > I thought that atomic_t is appropriate here. Valentin wanted to > > implement "window" and he needed to ensure that this window is counted > > correctly while it doesn't need to be 100% accurate. > > It does need to be 100% accurate because the stop_queue condition is: > > + if (atomic_read(&priv->tx_outstanding) == ipoib_sendq_size - 1) { So better to write ">=" instead of "=". > > And presumably the whole problem here is overflowing some sized q > opbject. > > That atomic is only needed if there is concurrency, and where is the > concurrency? Depends on if you believe to description in commit message :) > > Jason
On Thu, Feb 13, 2020 at 08:36:22PM +0200, Leon Romanovsky wrote: > On Thu, Feb 13, 2020 at 02:26:55PM -0400, Jason Gunthorpe wrote: > > On Thu, Feb 13, 2020 at 08:10:12PM +0200, Leon Romanovsky wrote: > > > On Thu, Feb 13, 2020 at 11:37:43AM -0400, Jason Gunthorpe wrote: > > > > On Wed, Feb 12, 2020 at 09:26:30AM +0200, Leon Romanovsky wrote: > > > > > > > > > diff --git a/drivers/infiniband/ulp/ipoib/ipoib.h b/drivers/infiniband/ulp/ipoib/ipoib.h > > > > > index 2aa3457a30ce..c614cb87d09b 100644 > > > > > +++ b/drivers/infiniband/ulp/ipoib/ipoib.h > > > > > @@ -379,6 +379,7 @@ struct ipoib_dev_priv { > > > > > struct ipoib_tx_buf *tx_ring; > > > > > unsigned int tx_head; > > > > > unsigned int tx_tail; > > > > > + atomic_t tx_outstanding; > > > > > struct ib_sge tx_sge[MAX_SKB_FRAGS + 1]; > > > > > struct ib_ud_wr tx_wr; > > > > > struct ib_wc send_wc[MAX_SEND_CQE]; > > > > > diff --git a/drivers/infiniband/ulp/ipoib/ipoib_cm.c b/drivers/infiniband/ulp/ipoib/ipoib_cm.c > > > > > index c59e00a0881f..db6aace83fe5 100644 > > > > > +++ b/drivers/infiniband/ulp/ipoib/ipoib_cm.c > > > > > @@ -756,7 +756,7 @@ void ipoib_cm_send(struct net_device *dev, struct sk_buff *skb, struct ipoib_cm_ > > > > > return; > > > > > } > > > > > > > > > > - if ((priv->tx_head - priv->tx_tail) == ipoib_sendq_size - 1) { > > > > > + if (atomic_read(&priv->tx_outstanding) == ipoib_sendq_size - 1) { > > > > > ipoib_dbg(priv, "TX ring 0x%x full, stopping kernel net queue\n", > > > > > tx->qp->qp_num); > > > > > netif_stop_queue(dev); > > > > > @@ -786,7 +786,7 @@ void ipoib_cm_send(struct net_device *dev, struct sk_buff *skb, struct ipoib_cm_ > > > > > } else { > > > > > netif_trans_update(dev); > > > > > ++tx->tx_head; > > > > > - ++priv->tx_head; > > > > > + atomic_inc(&priv->tx_outstanding); > > > > > } > > > > > > > > This use of an atomic is very weird, probably wrong. > > > > > > > > Why is it an atomic? priv->tx_head wasn't an atomic, and every place > > > > touching tx_outstanding was also touching tx_head. > > > > > > > > I assume there is some hidden locking here? Or much more stuff is > > > > busted up. > > > > > > > > In that case, drop the atomic. > > > > > > > > However, if the atomic is needed (where/why?) then something has to > > > > be dealing with the races, and if the write side is fully locked then > > > > an atomic is the wrong choice, use READ_ONCE/WRITE_ONCE instead > > > > > > I thought that atomic_t is appropriate here. Valentin wanted to > > > implement "window" and he needed to ensure that this window is counted > > > correctly while it doesn't need to be 100% accurate. > > > > It does need to be 100% accurate because the stop_queue condition is: > > > > + if (atomic_read(&priv->tx_outstanding) == ipoib_sendq_size - 1) { > > So better to write ">=" instead of "=". Then you risk overflowing the send q. The required scheme appears to be to globally bound the # of packets outstanding to tx such that the global bound is lower than any of the (many) QP's sendq, thus there will always be a place to put the packets. So it must be exact or at least pessimistic. This isn't a multiq netdev, so AFAICT, the tx side is single threaded by netdev, and it looks like the wc side was single threaded by NAPI as well. The old code used two variable, each written in a single threaded way, and then read to generate the state. With the missing READ_ONCE added, it should look like this: if ((priv->tx_head - READ_ONCE(priv->tx_tail)) == ipoib_sendq_size - 1) { I feel like sticking with the single writer packets posted/completed scheme is better and clearer than trying to collapse it into a single atomic. > > And presumably the whole problem here is overflowing some sized q > > opbject. > > > > That atomic is only needed if there is concurrency, and where is the > > concurrency? > > Depends on if you believe to description in commit message :) I do.. It is obviously wrong now that you point to it :) Each QP must have exclusive control of its head/tail pointers, having a CM QP reach into the head/tail of the UD QP is certainly wrong. Jason
diff --git a/drivers/infiniband/ulp/ipoib/ipoib.h b/drivers/infiniband/ulp/ipoib/ipoib.h index 2aa3457a30ce..c614cb87d09b 100644 --- a/drivers/infiniband/ulp/ipoib/ipoib.h +++ b/drivers/infiniband/ulp/ipoib/ipoib.h @@ -379,6 +379,7 @@ struct ipoib_dev_priv { struct ipoib_tx_buf *tx_ring; unsigned int tx_head; unsigned int tx_tail; + atomic_t tx_outstanding; struct ib_sge tx_sge[MAX_SKB_FRAGS + 1]; struct ib_ud_wr tx_wr; struct ib_wc send_wc[MAX_SEND_CQE]; diff --git a/drivers/infiniband/ulp/ipoib/ipoib_cm.c b/drivers/infiniband/ulp/ipoib/ipoib_cm.c index c59e00a0881f..db6aace83fe5 100644 --- a/drivers/infiniband/ulp/ipoib/ipoib_cm.c +++ b/drivers/infiniband/ulp/ipoib/ipoib_cm.c @@ -756,7 +756,7 @@ void ipoib_cm_send(struct net_device *dev, struct sk_buff *skb, struct ipoib_cm_ return; } - if ((priv->tx_head - priv->tx_tail) == ipoib_sendq_size - 1) { + if (atomic_read(&priv->tx_outstanding) == ipoib_sendq_size - 1) { ipoib_dbg(priv, "TX ring 0x%x full, stopping kernel net queue\n", tx->qp->qp_num); netif_stop_queue(dev); @@ -786,7 +786,7 @@ void ipoib_cm_send(struct net_device *dev, struct sk_buff *skb, struct ipoib_cm_ } else { netif_trans_update(dev); ++tx->tx_head; - ++priv->tx_head; + atomic_inc(&priv->tx_outstanding); } } @@ -820,11 +820,11 @@ void ipoib_cm_handle_tx_wc(struct net_device *dev, struct ib_wc *wc) netif_tx_lock(dev); ++tx->tx_tail; - ++priv->tx_tail; + atomic_dec(&priv->tx_outstanding); if (unlikely(netif_queue_stopped(dev) && - (priv->tx_head - priv->tx_tail) <= ipoib_sendq_size >> 1 && - test_bit(IPOIB_FLAG_ADMIN_UP, &priv->flags))) + (atomic_read(&priv->tx_outstanding) <= ipoib_sendq_size >> 1) && + test_bit(IPOIB_FLAG_ADMIN_UP, &priv->flags))) netif_wake_queue(dev); if (wc->status != IB_WC_SUCCESS && @@ -1232,8 +1232,9 @@ static void ipoib_cm_tx_destroy(struct ipoib_cm_tx *p) dev_kfree_skb_any(tx_req->skb); netif_tx_lock_bh(p->dev); ++p->tx_tail; - ++priv->tx_tail; - if (unlikely(priv->tx_head - priv->tx_tail == ipoib_sendq_size >> 1) && + atomic_dec(&priv->tx_outstanding); + if (unlikely(atomic_read(&priv->tx_outstanding) <= + ipoib_sendq_size >> 1) && netif_queue_stopped(p->dev) && test_bit(IPOIB_FLAG_ADMIN_UP, &priv->flags)) netif_wake_queue(p->dev); diff --git a/drivers/infiniband/ulp/ipoib/ipoib_ib.c b/drivers/infiniband/ulp/ipoib/ipoib_ib.c index c332b4761816..0652f25e8d0f 100644 --- a/drivers/infiniband/ulp/ipoib/ipoib_ib.c +++ b/drivers/infiniband/ulp/ipoib/ipoib_ib.c @@ -407,9 +407,11 @@ static void ipoib_ib_handle_tx_wc(struct net_device *dev, struct ib_wc *wc) dev_kfree_skb_any(tx_req->skb); ++priv->tx_tail; + atomic_dec(&priv->tx_outstanding); if (unlikely(netif_queue_stopped(dev) && - ((priv->tx_head - priv->tx_tail) <= ipoib_sendq_size >> 1) && + (atomic_read(&priv->tx_outstanding) <= ipoib_sendq_size >> + 1) && test_bit(IPOIB_FLAG_ADMIN_UP, &priv->flags))) netif_wake_queue(dev); @@ -634,7 +636,7 @@ int ipoib_send(struct net_device *dev, struct sk_buff *skb, else priv->tx_wr.wr.send_flags &= ~IB_SEND_IP_CSUM; /* increase the tx_head after send success, but use it for queue state */ - if (priv->tx_head - priv->tx_tail == ipoib_sendq_size - 1) { + if (atomic_read(&priv->tx_outstanding) == ipoib_sendq_size - 1) { ipoib_dbg(priv, "TX ring full, stopping kernel net queue\n"); netif_stop_queue(dev); } @@ -662,6 +664,7 @@ int ipoib_send(struct net_device *dev, struct sk_buff *skb, rc = priv->tx_head; ++priv->tx_head; + atomic_inc(&priv->tx_outstanding); } return rc; } @@ -807,6 +810,7 @@ int ipoib_ib_dev_stop_default(struct net_device *dev) ipoib_dma_unmap_tx(priv, tx_req); dev_kfree_skb_any(tx_req->skb); ++priv->tx_tail; + atomic_dec(&priv->tx_outstanding); } for (i = 0; i < ipoib_recvq_size; ++i) { diff --git a/drivers/infiniband/ulp/ipoib/ipoib_main.c b/drivers/infiniband/ulp/ipoib/ipoib_main.c index 4a0d3a9e72e1..0d98886cfef8 100644 --- a/drivers/infiniband/ulp/ipoib/ipoib_main.c +++ b/drivers/infiniband/ulp/ipoib/ipoib_main.c @@ -1706,6 +1706,7 @@ static int ipoib_dev_init_default(struct net_device *dev) } /* priv->tx_head, tx_tail & tx_outstanding are already 0 */ + atomic_set(&priv->tx_outstanding, 0); if (ipoib_transport_dev_init(dev, priv->ca)) { pr_warn("%s: ipoib_transport_dev_init failed\n",