Re: [PATCH v4] virtio_net: suppress cpu stall when free_unused_bufs

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在 2023/5/7 21:34, Michael S. Tsirkin 写道:
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@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx>
-add need_resched check.
-apply same logic to sq.
-use cond_resched instead.
-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?


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.



         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();


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