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

From: Jason Wang <jasowang@redhat.com>
To: mst@redhat.com, jasowang@redhat.com, davem@davemloft.net,
	edumazet@google.com, kuba@kernel.org, pabeni@redhat.com
Cc: netdev@vger.kernel.org, gautam.dawar@xilinx.com,
	linux-kernel@vger.kernel.org,
	virtualization@lists.linux-foundation.org
Subject: [PATCH net] virtio-net: add cond_resched() to the command waiting loop
Date: Mon,  5 Sep 2022 12:53:41 +0800	[thread overview]
Message-ID: <20220905045341.66191-1-jasowang@redhat.com> (raw)

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@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();
+	}
 
 	return vi->ctrl->status == VIRTIO_NET_OK;
 }
-- 
2.25.1

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