* [PATCH net-next]vhost: fix condition check for # of outstanding dma buffers @ 2011-07-19 18:37 Shirley Ma 2011-07-19 19:09 ` Michael S. Tsirkin 0 siblings, 1 reply; 7+ messages in thread From: Shirley Ma @ 2011-07-19 18:37 UTC (permalink / raw) To: David Miller, mst; +Cc: netdev, jasowang Signed-off-by: Shirley Ma <xma@us.ibm.com> --- drivers/vhost/net.c | 6 ++++-- 1 files changed, 4 insertions(+), 2 deletions(-) diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c index 70ac604..83cb738 100644 --- a/drivers/vhost/net.c +++ b/drivers/vhost/net.c @@ -189,8 +189,10 @@ static void handle_tx(struct vhost_net *net) break; } /* If more outstanding DMAs, queue the work */ - if (unlikely(vq->upend_idx - vq->done_idx > - VHOST_MAX_PEND)) { + if (unlikely((vq->upend_idx - vq->done_idx > + VHOST_MAX_PEND) || + (vq->upend_idx - vq->done_idx > + VHOST_MAX_PEND - UIO_MAXIOV))) { tx_poll_start(net, sock); set_bit(SOCK_ASYNC_NOSPACE, &sock->flags); break; ^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [PATCH net-next]vhost: fix condition check for # of outstanding dma buffers 2011-07-19 18:37 [PATCH net-next]vhost: fix condition check for # of outstanding dma buffers Shirley Ma @ 2011-07-19 19:09 ` Michael S. Tsirkin 2011-07-19 20:56 ` Shirley Ma 0 siblings, 1 reply; 7+ messages in thread From: Michael S. Tsirkin @ 2011-07-19 19:09 UTC (permalink / raw) To: Shirley Ma; +Cc: David Miller, netdev, jasowang On Tue, Jul 19, 2011 at 11:37:58AM -0700, Shirley Ma wrote: > Signed-off-by: Shirley Ma <xma@us.ibm.com> > --- > > drivers/vhost/net.c | 6 ++++-- > 1 files changed, 4 insertions(+), 2 deletions(-) > > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c > index 70ac604..83cb738 100644 > --- a/drivers/vhost/net.c > +++ b/drivers/vhost/net.c > @@ -189,8 +189,10 @@ static void handle_tx(struct vhost_net *net) > break; > } > /* If more outstanding DMAs, queue the work */ > - if (unlikely(vq->upend_idx - vq->done_idx > > - VHOST_MAX_PEND)) { > + if (unlikely((vq->upend_idx - vq->done_idx > > + VHOST_MAX_PEND) || > + (vq->upend_idx - vq->done_idx > > + VHOST_MAX_PEND - UIO_MAXIOV))) { Could you please explain why this makes sense please? VHOST_MAX_PEND is 128 UIO_MAXIOV is 1024 so the result is negative? I thought upend_idx - done_idx is exactly the number of buffers, so once we get too many we stop until one gets freed? > tx_poll_start(net, sock); > set_bit(SOCK_ASYNC_NOSPACE, &sock->flags); > break; > ^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH net-next]vhost: fix condition check for # of outstanding dma buffers 2011-07-19 19:09 ` Michael S. Tsirkin @ 2011-07-19 20:56 ` Shirley Ma 2011-07-20 10:28 ` Michael S. Tsirkin 0 siblings, 1 reply; 7+ messages in thread From: Shirley Ma @ 2011-07-19 20:56 UTC (permalink / raw) To: Michael S. Tsirkin; +Cc: David Miller, netdev, jasowang On Tue, 2011-07-19 at 22:09 +0300, Michael S. Tsirkin wrote: > On Tue, Jul 19, 2011 at 11:37:58AM -0700, Shirley Ma wrote: > > Signed-off-by: Shirley Ma <xma@us.ibm.com> > > --- > > > > drivers/vhost/net.c | 6 ++++-- > > 1 files changed, 4 insertions(+), 2 deletions(-) > > > > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c > > index 70ac604..83cb738 100644 > > --- a/drivers/vhost/net.c > > +++ b/drivers/vhost/net.c > > @@ -189,8 +189,10 @@ static void handle_tx(struct vhost_net *net) > > break; > > } > > /* If more outstanding DMAs, queue the work */ > > - if (unlikely(vq->upend_idx - vq->done_idx > > > - VHOST_MAX_PEND)) { > > + if (unlikely((vq->upend_idx - vq->done_idx > > > + VHOST_MAX_PEND) || > > + (vq->upend_idx - vq->done_idx > > > + VHOST_MAX_PEND - > UIO_MAXIOV))) { > > Could you please explain why this makes sense please? > VHOST_MAX_PEND is 128 UIO_MAXIOV is 1024 so > the result is negative? I thought it is equal to: if (vq->upend_idx > vq->done_idx) check vq->upend_idx - vq->done_idx > VHOST_MAX_PEND if (vq->upend_idx < vq->done_idx) check vq->upend_idx + UIO_MAXIOV - vq->done_idx > VHOST_MAX_PEND > I thought upend_idx - done_idx is exactly the number > of buffers, so once we get too many we stop until > one gets freed? They are index, so in vhost zerocopy callback, we can get the idx right away. > > > tx_poll_start(net, sock); > > set_bit(SOCK_ASYNC_NOSPACE, > &sock->flags); > > break; > > ^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH net-next]vhost: fix condition check for # of outstanding dma buffers 2011-07-19 20:56 ` Shirley Ma @ 2011-07-20 10:28 ` Michael S. Tsirkin 2011-07-20 15:43 ` Shirley Ma 0 siblings, 1 reply; 7+ messages in thread From: Michael S. Tsirkin @ 2011-07-20 10:28 UTC (permalink / raw) To: Shirley Ma; +Cc: David Miller, netdev, jasowang On Tue, Jul 19, 2011 at 01:56:25PM -0700, Shirley Ma wrote: > On Tue, 2011-07-19 at 22:09 +0300, Michael S. Tsirkin wrote: > > On Tue, Jul 19, 2011 at 11:37:58AM -0700, Shirley Ma wrote: > > > Signed-off-by: Shirley Ma <xma@us.ibm.com> > > > --- > > > > > > drivers/vhost/net.c | 6 ++++-- > > > 1 files changed, 4 insertions(+), 2 deletions(-) > > > > > > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c > > > index 70ac604..83cb738 100644 > > > --- a/drivers/vhost/net.c > > > +++ b/drivers/vhost/net.c > > > @@ -189,8 +189,10 @@ static void handle_tx(struct vhost_net *net) > > > break; > > > } > > > /* If more outstanding DMAs, queue the work */ > > > - if (unlikely(vq->upend_idx - vq->done_idx > > > > - VHOST_MAX_PEND)) { > > > + if (unlikely((vq->upend_idx - vq->done_idx > > > > + VHOST_MAX_PEND) || > > > + (vq->upend_idx - vq->done_idx > > > > + VHOST_MAX_PEND - > > UIO_MAXIOV))) { > > > > Could you please explain why this makes sense please? > > VHOST_MAX_PEND is 128 UIO_MAXIOV is 1024 so > > the result is negative? > > I thought it is equal to: > > if (vq->upend_idx > vq->done_idx) > check vq->upend_idx - vq->done_idx > VHOST_MAX_PEND > if (vq->upend_idx < vq->done_idx) > check vq->upend_idx + UIO_MAXIOV - vq->done_idx > VHOST_MAX_PEND > Check it out: upend_idx == done_idx == 0 does not satisfy the above conditions but does trigger in your code, right? Better keep it simple. Maybe: if (unlikely(vq->upend_idx - vq->done_idx > VHOST_MAX_PEND) || (unlikely(vq->upend_idx < vq->done_idx) && unlikely(vq->upend_idx + UIO_MAXIOV - vq->done_idx > VHOST_MAX_PEND))) ? Also, please add commit log documenting what does the patch fix: something like: 'the test for # of outstanding buffers returned incorrect results when due to wrap around, upend_idx < done_idx'? > > I thought upend_idx - done_idx is exactly the number > > of buffers, so once we get too many we stop until > > one gets freed? > > They are index, so in vhost zerocopy callback, we can get the idx right > away. > > > > > > tx_poll_start(net, sock); > > > set_bit(SOCK_ASYNC_NOSPACE, > > &sock->flags); > > > break; > > > ^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH net-next]vhost: fix condition check for # of outstanding dma buffers 2011-07-20 10:28 ` Michael S. Tsirkin @ 2011-07-20 15:43 ` Shirley Ma 2011-07-20 16:17 ` Michael S. Tsirkin 0 siblings, 1 reply; 7+ messages in thread From: Shirley Ma @ 2011-07-20 15:43 UTC (permalink / raw) To: Michael S. Tsirkin; +Cc: David Miller, netdev, jasowang On Wed, 2011-07-20 at 13:28 +0300, Michael S. Tsirkin wrote: > On Tue, Jul 19, 2011 at 01:56:25PM -0700, Shirley Ma wrote: > > On Tue, 2011-07-19 at 22:09 +0300, Michael S. Tsirkin wrote: > > > On Tue, Jul 19, 2011 at 11:37:58AM -0700, Shirley Ma wrote: > > > > Signed-off-by: Shirley Ma <xma@us.ibm.com> > > > > --- > > > > > > > > drivers/vhost/net.c | 6 ++++-- > > > > 1 files changed, 4 insertions(+), 2 deletions(-) > > > > > > > > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c > > > > index 70ac604..83cb738 100644 > > > > --- a/drivers/vhost/net.c > > > > +++ b/drivers/vhost/net.c > > > > @@ -189,8 +189,10 @@ static void handle_tx(struct vhost_net > *net) > > > > break; > > > > } > > > > /* If more outstanding DMAs, queue the > work */ > > > > - if (unlikely(vq->upend_idx - vq->done_idx > > > > > > - VHOST_MAX_PEND)) { > > > > + if (unlikely((vq->upend_idx - vq->done_idx > > > > > > + VHOST_MAX_PEND) || > > > > + (vq->upend_idx - vq->done_idx > > > > > > + VHOST_MAX_PEND - > > > UIO_MAXIOV))) { > > > > > > Could you please explain why this makes sense please? > > > VHOST_MAX_PEND is 128 UIO_MAXIOV is 1024 so > > > the result is negative? > > > > I thought it is equal to: > > > > if (vq->upend_idx > vq->done_idx) > > check vq->upend_idx - vq->done_idx > VHOST_MAX_PEND > > if (vq->upend_idx < vq->done_idx) > > check vq->upend_idx + UIO_MAXIOV - vq->done_idx > > VHOST_MAX_PEND > > > > Check it out: upend_idx == done_idx == 0 does not satisfy the > above conditions but does trigger in your code, right? We don't hit upend_idx == done_idx == 0. Only upend_idx == done_idx == UIO_MAXIOV could happen if the lower device has issue and never DMA any packets out. > Better keep it simple. Maybe: > > if (unlikely(vq->upend_idx - vq->done_idx > VHOST_MAX_PEND) || > (unlikely(vq->upend_idx < vq->done_idx) && > unlikely(vq->upend_idx + UIO_MAXIOV - vq->done_idx > > VHOST_MAX_PEND))) > > ? > > Also, please add commit log documenting what does the patch > fix: something like: > 'the test for # of outstanding buffers returned > incorrect results when due to wrap around, > upend_idx < done_idx'? Sure, will modify it and resubmit. > > > I thought upend_idx - done_idx is exactly the number > > > of buffers, so once we get too many we stop until > > > one gets freed? > > > > They are index, so in vhost zerocopy callback, we can get the idx > right > > away. > > > > > > > > > tx_poll_start(net, sock); > > > > set_bit(SOCK_ASYNC_NOSPACE, > > > &sock->flags); > > > > break; > > > > Thanks Shirley ^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH net-next]vhost: fix condition check for # of outstanding dma buffers 2011-07-20 15:43 ` Shirley Ma @ 2011-07-20 16:17 ` Michael S. Tsirkin 2011-07-20 16:49 ` Shirley Ma 0 siblings, 1 reply; 7+ messages in thread From: Michael S. Tsirkin @ 2011-07-20 16:17 UTC (permalink / raw) To: Shirley Ma; +Cc: David Miller, netdev, jasowang On Wed, Jul 20, 2011 at 08:43:09AM -0700, Shirley Ma wrote: > On Wed, 2011-07-20 at 13:28 +0300, Michael S. Tsirkin wrote: > > On Tue, Jul 19, 2011 at 01:56:25PM -0700, Shirley Ma wrote: > > > On Tue, 2011-07-19 at 22:09 +0300, Michael S. Tsirkin wrote: > > > > On Tue, Jul 19, 2011 at 11:37:58AM -0700, Shirley Ma wrote: > > > > > Signed-off-by: Shirley Ma <xma@us.ibm.com> > > > > > --- > > > > > > > > > > drivers/vhost/net.c | 6 ++++-- > > > > > 1 files changed, 4 insertions(+), 2 deletions(-) > > > > > > > > > > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c > > > > > index 70ac604..83cb738 100644 > > > > > --- a/drivers/vhost/net.c > > > > > +++ b/drivers/vhost/net.c > > > > > @@ -189,8 +189,10 @@ static void handle_tx(struct vhost_net > > *net) > > > > > break; > > > > > } > > > > > /* If more outstanding DMAs, queue the > > work */ > > > > > - if (unlikely(vq->upend_idx - vq->done_idx > > > > > > > > - VHOST_MAX_PEND)) { > > > > > + if (unlikely((vq->upend_idx - vq->done_idx > > > > > > > > + VHOST_MAX_PEND) || > > > > > + (vq->upend_idx - vq->done_idx > > > > > > > > + VHOST_MAX_PEND - > > > > UIO_MAXIOV))) { > > > > > > > > Could you please explain why this makes sense please? > > > > VHOST_MAX_PEND is 128 UIO_MAXIOV is 1024 so > > > > the result is negative? > > > > > > I thought it is equal to: > > > > > > if (vq->upend_idx > vq->done_idx) > > > check vq->upend_idx - vq->done_idx > VHOST_MAX_PEND > > > if (vq->upend_idx < vq->done_idx) > > > check vq->upend_idx + UIO_MAXIOV - vq->done_idx > > > VHOST_MAX_PEND > > > > > > > Check it out: upend_idx == done_idx == 0 does not satisfy the > > above conditions but does trigger in your code, right? > > We don't hit upend_idx == done_idx == 0. Only upend_idx == done_idx == > UIO_MAXIOV could happen if the lower device has issue and never DMA any > packets out. My point was that the logic isn't the same, even though you said 'it is equal to'. Same applies to upend_idx == 1, done_idx == 0. > > Better keep it simple. Maybe: > > > > if (unlikely(vq->upend_idx - vq->done_idx > VHOST_MAX_PEND) || > > (unlikely(vq->upend_idx < vq->done_idx) && > > unlikely(vq->upend_idx + UIO_MAXIOV - vq->done_idx > > > VHOST_MAX_PEND))) > > > > ? > > > > Also, please add commit log documenting what does the patch > > fix: something like: > > 'the test for # of outstanding buffers returned > > incorrect results when due to wrap around, > > upend_idx < done_idx'? > > Sure, will modify it and resubmit. > > > > > I thought upend_idx - done_idx is exactly the number > > > > of buffers, so once we get too many we stop until > > > > one gets freed? > > > > > > They are index, so in vhost zerocopy callback, we can get the idx > > right > > > away. > > > > > > > > > > > > tx_poll_start(net, sock); > > > > > set_bit(SOCK_ASYNC_NOSPACE, > > > > &sock->flags); > > > > > break; > > > > > > > Thanks > Shirley ^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH net-next]vhost: fix condition check for # of outstanding dma buffers 2011-07-20 16:17 ` Michael S. Tsirkin @ 2011-07-20 16:49 ` Shirley Ma 0 siblings, 0 replies; 7+ messages in thread From: Shirley Ma @ 2011-07-20 16:49 UTC (permalink / raw) To: Michael S. Tsirkin; +Cc: David Miller, netdev, jasowang On Wed, 2011-07-20 at 19:17 +0300, Michael S. Tsirkin wrote: > My point was that the logic isn't the same, even though > you said 'it is equal to'. > Same applies to upend_idx == 1, done_idx == 0. :) not sure what I was thinking. I will resubmit the patch. Thanks Shirley ^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2011-07-20 16:49 UTC | newest] Thread overview: 7+ messages (download: mbox.gz follow: Atom feed -- links below jump to the message on this page -- 2011-07-19 18:37 [PATCH net-next]vhost: fix condition check for # of outstanding dma buffers Shirley Ma 2011-07-19 19:09 ` Michael S. Tsirkin 2011-07-19 20:56 ` Shirley Ma 2011-07-20 10:28 ` Michael S. Tsirkin 2011-07-20 15:43 ` Shirley Ma 2011-07-20 16:17 ` Michael S. Tsirkin 2011-07-20 16:49 ` Shirley Ma
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