Michael S. Tsirkin
2023-May-08 06:07 UTC
[PATCH v4] virtio_net: suppress cpu stall when free_unused_bufs
On Mon, May 08, 2023 at 11:12:03AM +0800, Jason Wang wrote:> > ? 2023/5/7 21:34, Michael S. Tsirkin ??: > > On Fri, May 05, 2023 at 11:28:25AM +0800, Jason Wang wrote: > > > On Thu, May 4, 2023 at 10:27?AM Wenliang Wang > > > <wangwenliang.1995 at bytedance.com> wrote: > > > > For multi-queue and large ring-size use case, the following error > > > > occurred when free_unused_bufs: > > > > rcu: INFO: rcu_sched self-detected stall on CPU. > > > > > > > > Fixes: 986a4f4d452d ("virtio_net: multiqueue support") > > > > Signed-off-by: Wenliang Wang <wangwenliang.1995 at bytedance.com> > > > > --- > > > > v2: > > > > -add need_resched check. > > > > -apply same logic to sq. > > > > v3: > > > > -use cond_resched instead. > > > > v4: > > > > -add fixes tag > > > > --- > > > > drivers/net/virtio_net.c | 2 ++ > > > > 1 file changed, 2 insertions(+) > > > > > > > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > > > > index 8d8038538fc4..a12ae26db0e2 100644 > > > > --- a/drivers/net/virtio_net.c > > > > +++ b/drivers/net/virtio_net.c > > > > @@ -3560,12 +3560,14 @@ static void free_unused_bufs(struct virtnet_info *vi) > > > > struct virtqueue *vq = vi->sq[i].vq; > > > > while ((buf = virtqueue_detach_unused_buf(vq)) != NULL) > > > > virtnet_sq_free_unused_buf(vq, buf); > > > > + cond_resched(); > > > Does this really address the case when the virtqueue is very large? > > > > > > Thanks > > > > it does in that a very large queue is still just 64k in size. > > we might however have 64k of these queues. > > > Ok, but we have other similar loops especially the refill, I think we may > need cond_resched() there as well. > > Thanks >Refill is already per vq isn't it?> > > > > > } > > > > > > > > for (i = 0; i < vi->max_queue_pairs; i++) { > > > > struct virtqueue *vq = vi->rq[i].vq; > > > > while ((buf = virtqueue_detach_unused_buf(vq)) != NULL) > > > > virtnet_rq_free_unused_buf(vq, buf); > > > > + cond_resched(); > > > > } > > > > } > > > > > > > > -- > > > > 2.20.1 > > > >
Jason Wang
2023-May-08 06:13 UTC
[PATCH v4] virtio_net: suppress cpu stall when free_unused_bufs
On Mon, May 8, 2023 at 2:08?PM Michael S. Tsirkin <mst at redhat.com> wrote:> > On Mon, May 08, 2023 at 11:12:03AM +0800, Jason Wang wrote: > > > > ? 2023/5/7 21:34, Michael S. Tsirkin ??: > > > On Fri, May 05, 2023 at 11:28:25AM +0800, Jason Wang wrote: > > > > On Thu, May 4, 2023 at 10:27?AM Wenliang Wang > > > > <wangwenliang.1995 at bytedance.com> wrote: > > > > > For multi-queue and large ring-size use case, the following error > > > > > occurred when free_unused_bufs: > > > > > rcu: INFO: rcu_sched self-detected stall on CPU. > > > > > > > > > > Fixes: 986a4f4d452d ("virtio_net: multiqueue support") > > > > > Signed-off-by: Wenliang Wang <wangwenliang.1995 at bytedance.com> > > > > > --- > > > > > v2: > > > > > -add need_resched check. > > > > > -apply same logic to sq. > > > > > v3: > > > > > -use cond_resched instead. > > > > > v4: > > > > > -add fixes tag > > > > > --- > > > > > drivers/net/virtio_net.c | 2 ++ > > > > > 1 file changed, 2 insertions(+) > > > > > > > > > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > > > > > index 8d8038538fc4..a12ae26db0e2 100644 > > > > > --- a/drivers/net/virtio_net.c > > > > > +++ b/drivers/net/virtio_net.c > > > > > @@ -3560,12 +3560,14 @@ static void free_unused_bufs(struct virtnet_info *vi) > > > > > struct virtqueue *vq = vi->sq[i].vq; > > > > > while ((buf = virtqueue_detach_unused_buf(vq)) != NULL) > > > > > virtnet_sq_free_unused_buf(vq, buf); > > > > > + cond_resched(); > > > > Does this really address the case when the virtqueue is very large? > > > > > > > > Thanks > > > > > > it does in that a very large queue is still just 64k in size. > > > we might however have 64k of these queues. > > > > > > Ok, but we have other similar loops especially the refill, I think we may > > need cond_resched() there as well. > > > > Thanks > > > > Refill is already per vq isn't it?Not for the refill_work(). Thanks> > > > > > > > > > } > > > > > > > > > > for (i = 0; i < vi->max_queue_pairs; i++) { > > > > > struct virtqueue *vq = vi->rq[i].vq; > > > > > while ((buf = virtqueue_detach_unused_buf(vq)) != NULL) > > > > > virtnet_rq_free_unused_buf(vq, buf); > > > > > + cond_resched(); > > > > > } > > > > > } > > > > > > > > > > -- > > > > > 2.20.1 > > > > > >