On Thu, Jul 20, 2023 at 08:31:13AM -0700, Shannon Nelson wrote:

On 7/20/23 1:38 AM, Jason Wang wrote:

quoted

Adding cond_resched() to the command waiting loop for a better
co-operation with the scheduler. This allows to give CPU a breath to
run other task(workqueue) instead of busy looping when preemption is
not allowed on a device whose CVQ might be slow.

Signed-off-by: Jason Wang <jasowang@redhat.com>
---
  drivers/net/virtio_net.c | 4 +++-
  1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 9f3b1d6ac33d..e7533f29b219 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c

@@ -2314,8 +2314,10 @@ static bool virtnet_send_command(struct virtnet_info *vi, u8 class, u8 cmd,
          * into the hypervisor, so the request should be handled immediately.
          */
         while (!virtqueue_get_buf(vi->cvq, &tmp) &&
-              !virtqueue_is_broken(vi->cvq))
+              !virtqueue_is_broken(vi->cvq)) {
+               cond_resched();
                 cpu_relax();
+       }

The cover letter suggests that this addresses the infinite poll for buggy
devices, but I don't see how that is resolved here.  This should make it a
little nicer to the system, but it still is going to poll forever on a
device that has gone catatonic.  Is there a reason that I'm missing that we
don't have a polling limit here?

sln

we don't know what the limit would be. but given it's a workqueue
now, why does it still have to poll as opposed to blocking?

quoted

         return vi->ctrl->status == VIRTIO_NET_OK;
  }
--
2.39.3

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