On Fri, Jul 21, 2023 at 04:58:04PM +0200, Maxime Coquelin wrote:

On 7/21/23 16:45, Michael S. Tsirkin wrote:

quoted

On Fri, Jul 21, 2023 at 04:37:00PM +0200, Maxime Coquelin wrote:

quoted

On 7/20/23 23:02, Michael S. Tsirkin wrote:

quoted

On Thu, Jul 20, 2023 at 01:26:20PM -0700, Shannon Nelson wrote:

quoted

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>

This still leaves hung processes, but at least it doesn't pin the CPU any
more.  Thanks.
Reviewed-by: Shannon Nelson <redacted>

I'd like to see a full solution
1- block until interrupt

Would it make sense to also have a timeout?
And when timeout expires, set FAILED bit in device status?

virtio spec does not set any limits on the timing of vq
processing.

Indeed, but I thought the driver could decide it is too long for it.

The issue is we keep waiting with rtnl locked, it can quickly make the
system unusable.

if this is a problem we should find a way not to keep rtnl
locked indefinitely.

quoted

quoted

quoted

2- still handle surprise removal correctly by waking in that case

quoted

quoted

---
    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();
+       }

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

2.39.3

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