linux-kernel - [PATCH net] virtio-net: add cond_resched() to the command waiting loop

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Message-Id: <20220905045341.66191-1-jasowang@redhat.com>
Date:   Mon,  5 Sep 2022 12:53:41 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     mst@...hat.com, jasowang@...hat.com, davem@...emloft.net,
        edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com
Cc:     gautam.dawar@...inx.com, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH net] virtio-net: add cond_resched() to the command waiting loop

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")
Signed-off-by: Jason Wang <jasowang@...hat.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();
+	}
 
 	return vi->ctrl->status == VIRTIO_NET_OK;
 }
-- 
2.25.1