On Mon, Sep 5, 2022 at 3:15 PM Michael S. Tsirkin [off-list ref] wrote:

On Mon, Sep 05, 2022 at 12:53:41PM +0800, 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.

What's more important. This is a must for some vDPA parent to work
since control virtqueue is emulated via a workqueue for those parents.

Fixes: bda324fd037a ("vdpasim: control virtqueue support")

That's a weird commit to fix. so it fixes the simulator?

Yes, since the simulator is using a workqueue to handle control virtueue.

quoted

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 ece00b84e3a7..169368365d6a 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c

@@ -2000,8 +2000,10 @@ 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();
+     }

with cond_resched do we still need cpu_relax?

I think so, it's possible that cond_sched() just doesn't trigger scheduling.

Thanks

quoted

      return vi->ctrl->status == VIRTIO_NET_OK;
 }
--
2.25.1