Re: [PATCH 24/33] virtio_net: xsk: stop disable tx napi

On Thu, 2 Feb 2023 12:25:59 -0500, "Michael S. Tsirkin" [off-list ref] wrote:

On Thu, Feb 02, 2023 at 07:00:49PM +0800, Xuan Zhuo wrote:

quoted

Since xsk's TX queue is consumed by TX NAPI, if sq is bound to xsk, then
we must stop tx napi from being disabled.

Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
---
 drivers/net/virtio/main.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/net/virtio/main.c b/drivers/net/virtio/main.c
index ed79e750bc6c..232cf151abff 100644
--- a/drivers/net/virtio/main.c
+++ b/drivers/net/virtio/main.c

@@ -2728,8 +2728,15 @@ static int virtnet_set_coalesce(struct net_device *dev,
 		return ret;

 	if (update_napi) {
-		for (i = 0; i < vi->max_queue_pairs; i++)
+		for (i = 0; i < vi->max_queue_pairs; i++) {
+			/* xsk xmit depend on the tx napi. So if xsk is active,

depends.

quoted

+			 * prevent modifications to tx napi.
+			 */
+			if (rtnl_dereference(vi->sq[i].xsk.pool))
+				continue;
+
 			vi->sq[i].napi.weight = napi_weight;

I don't get it.
changing napi weight does not work then.
why is this ok?

static void skb_xmit_done(struct virtqueue *vq)
{
	struct virtnet_info *vi = vq->vdev->priv;
	struct napi_struct *napi = &vi->sq[vq2txq(vq)].napi;

	/* Suppress further interrupts. */
	virtqueue_disable_cb(vq);

	if (napi->weight)
		virtqueue_napi_schedule(napi, vq);
	else
		/* We were probably waiting for more output buffers. */
		netif_wake_subqueue(vi->dev, vq2txq(vq));
}


If the weight is 0, tx napi will not be triggered again.

Thanks.

quoted

+		}
 	}

 	return ret;
--
2.32.0.3.g01195cf9f

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