linux-kernel - [PATCH v3 3/3] vhost-net: flush batched before enabling notifications

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Message-ID: <7b0c9cf7c81e39a59897b3a76d159aa0580b2baa.1757952021.git.mst@redhat.com>
Date: Mon, 15 Sep 2025 12:03:27 -0400
From: "Michael S. Tsirkin" <mst@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: Jon Kohler <jon@...anix.com>, netdev@...r.kernel.org,
	stable@...r.kernel.org, Jason Wang <jasowang@...hat.com>,
	Eugenio Pérez <eperezma@...hat.com>,
	Jakub Kicinski <kuba@...nel.org>, kvm@...r.kernel.org,
	virtualization@...ts.linux.dev
Subject: [PATCH v3 3/3] vhost-net: flush batched before enabling notifications

Commit 8c2e6b26ffe2 ("vhost/net: Defer TX queue re-enable until after
sendmsg") tries to defer the notification enabling by moving the logic
out of the loop after the vhost_tx_batch() when nothing new is spotted.
This caused unexpected side effects as the new logic is reused for
several other error conditions.

A previous patch reverted 8c2e6b26ffe2. Now, bring the performance
back up by flushing batched buffers before enabling notifications.

Link: https://lore.kernel.org/all/20250915024703.2206-2-jasowang@redhat.com
Reported-by: Jon Kohler <jon@...anix.com>
Cc: stable@...r.kernel.org
Fixes: 8c2e6b26ffe2 ("vhost/net: Defer TX queue re-enable until after sendmsg")
Signed-off-by: Jason Wang <jasowang@...hat.com>
Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
---
 drivers/vhost/net.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 57efd5c55f89..72ecb8691275 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -782,11 +782,18 @@ static void handle_tx_copy(struct vhost_net *net, struct socket *sock)
 		if (head == vq->num) {
 			if (unlikely(busyloop_intr)) {
 				vhost_poll_queue(&vq->poll);
-			} else if (unlikely(vhost_enable_notify(&net->dev,
-								vq))) {
-				vhost_disable_notify(&net->dev, vq);
-				continue;
-			}
+			} else {
+				/* Flush batched packets before enabling
+				 * virtqueue notifications to reduce
+				 * unnecessary virtqueue kicks.
+				 */
+				vhost_tx_batch(net, nvq, sock, &msg);
+
+				if (unlikely(vhost_enable_notify(&net->dev,
+								 vq))) {
+					vhost_disable_notify(&net->dev, vq);
+					continue;
+				}
 			break;
 		}
 
-- 
MST