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From: "Michael S. Tsirkin" <mst@redhat.com>
To: linux-kernel@vger.kernel.org
Cc: Jakub Kicinski <kuba@kernel.org>, Wei Wang <weiwan@google.com>,
	David Miller <davem@davemloft.net>,
	netdev@vger.kernel.org, Willem de Bruijn <willemb@google.com>,
	virtualization@lists.linux-foundation.org,
	Jason Wang <jasowang@redhat.com>
Subject: [PATCH v3 2/4] virtio_net: move txq wakeups under tx q lock
Date: Wed, 26 May 2021 04:24:37 -0400	[thread overview]
Message-ID: <20210526082423.47837-3-mst@redhat.com> (raw)
In-Reply-To: <20210526082423.47837-1-mst@redhat.com>

We currently check num_free outside tx q lock
which is unsafe: new packets can arrive meanwhile
and there won't be space in the queue.
Thus a spurious queue wakeup causing overhead
and even packet drops.

Move the check under the lock to fix that.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 drivers/net/virtio_net.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 12512d1002ec..c29f42d1e04f 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -1434,11 +1434,12 @@ static void virtnet_poll_cleantx(struct receive_queue *rq)
 
 	if (__netif_tx_trylock(txq)) {
 		free_old_xmit_skbs(sq, true);
+
+		if (sq->vq->num_free >= 2 + MAX_SKB_FRAGS)
+			netif_tx_wake_queue(txq);
+
 		__netif_tx_unlock(txq);
 	}
-
-	if (sq->vq->num_free >= 2 + MAX_SKB_FRAGS)
-		netif_tx_wake_queue(txq);
 }
 
 static int virtnet_poll(struct napi_struct *napi, int budget)
@@ -1522,6 +1523,9 @@ static int virtnet_poll_tx(struct napi_struct *napi, int budget)
 	virtqueue_disable_cb(sq->vq);
 	free_old_xmit_skbs(sq, true);
 
+	if (sq->vq->num_free >= 2 + MAX_SKB_FRAGS)
+		netif_tx_wake_queue(txq);
+
 	opaque = virtqueue_enable_cb_prepare(sq->vq);
 
 	done = napi_complete_done(napi, 0);
@@ -1542,9 +1546,6 @@ static int virtnet_poll_tx(struct napi_struct *napi, int budget)
 		}
 	}
 
-	if (sq->vq->num_free >= 2 + MAX_SKB_FRAGS)
-		netif_tx_wake_queue(txq);
-
 	return 0;
 }
 
-- 
MST


WARNING: multiple messages have this Message-ID (diff)
From: "Michael S. Tsirkin" <mst@redhat.com>
To: linux-kernel@vger.kernel.org
Cc: Willem de Bruijn <willemb@google.com>,
	netdev@vger.kernel.org,
	virtualization@lists.linux-foundation.org,
	Jakub Kicinski <kuba@kernel.org>, Wei Wang <weiwan@google.com>,
	David Miller <davem@davemloft.net>
Subject: [PATCH v3 2/4] virtio_net: move txq wakeups under tx q lock
Date: Wed, 26 May 2021 04:24:37 -0400	[thread overview]
Message-ID: <20210526082423.47837-3-mst@redhat.com> (raw)
In-Reply-To: <20210526082423.47837-1-mst@redhat.com>

We currently check num_free outside tx q lock
which is unsafe: new packets can arrive meanwhile
and there won't be space in the queue.
Thus a spurious queue wakeup causing overhead
and even packet drops.

Move the check under the lock to fix that.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 drivers/net/virtio_net.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 12512d1002ec..c29f42d1e04f 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -1434,11 +1434,12 @@ static void virtnet_poll_cleantx(struct receive_queue *rq)
 
 	if (__netif_tx_trylock(txq)) {
 		free_old_xmit_skbs(sq, true);
+
+		if (sq->vq->num_free >= 2 + MAX_SKB_FRAGS)
+			netif_tx_wake_queue(txq);
+
 		__netif_tx_unlock(txq);
 	}
-
-	if (sq->vq->num_free >= 2 + MAX_SKB_FRAGS)
-		netif_tx_wake_queue(txq);
 }
 
 static int virtnet_poll(struct napi_struct *napi, int budget)
@@ -1522,6 +1523,9 @@ static int virtnet_poll_tx(struct napi_struct *napi, int budget)
 	virtqueue_disable_cb(sq->vq);
 	free_old_xmit_skbs(sq, true);
 
+	if (sq->vq->num_free >= 2 + MAX_SKB_FRAGS)
+		netif_tx_wake_queue(txq);
+
 	opaque = virtqueue_enable_cb_prepare(sq->vq);
 
 	done = napi_complete_done(napi, 0);
@@ -1542,9 +1546,6 @@ static int virtnet_poll_tx(struct napi_struct *napi, int budget)
 		}
 	}
 
-	if (sq->vq->num_free >= 2 + MAX_SKB_FRAGS)
-		netif_tx_wake_queue(txq);
-
 	return 0;
 }
 
-- 
MST

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  parent reply	other threads:[~2021-05-26  8:24 UTC|newest]

Thread overview: 49+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-26  8:24 [PATCH v3 0/4] virtio net: spurious interrupt related fixes Michael S. Tsirkin
2021-05-26  8:24 ` Michael S. Tsirkin
2021-05-26  8:24 ` [PATCH v3 1/4] virtio_net: move tx vq operation under tx queue lock Michael S. Tsirkin
2021-05-26  8:24   ` Michael S. Tsirkin
2021-05-27  3:41   ` Jason Wang
2021-05-27  3:41     ` Jason Wang
2021-05-28 22:25     ` Willem de Bruijn
2021-05-28 22:25       ` Willem de Bruijn
2021-06-09 22:03       ` Michael S. Tsirkin
2021-06-09 22:03         ` Michael S. Tsirkin
2021-05-26  8:24 ` Michael S. Tsirkin [this message]
2021-05-26  8:24   ` [PATCH v3 2/4] virtio_net: move txq wakeups under tx q lock Michael S. Tsirkin
2021-05-27  3:48   ` Jason Wang
2021-05-27  3:48     ` Jason Wang
2021-05-26  8:24 ` [PATCH v3 3/4] virtio: fix up virtio_disable_cb Michael S. Tsirkin
2021-05-26  8:24   ` Michael S. Tsirkin
2021-05-27  4:01   ` Jason Wang
2021-05-27  4:01     ` Jason Wang
2023-03-30  6:07   ` Xuan Zhuo
2023-03-30  6:07     ` Xuan Zhuo
2023-03-30  6:44     ` Michael S. Tsirkin
2023-03-30  6:44       ` Michael S. Tsirkin
2023-03-30  6:54       ` Xuan Zhuo
2023-03-30  6:54         ` Xuan Zhuo
2023-03-30 14:04         ` Michael S. Tsirkin
2023-03-30 14:04           ` Michael S. Tsirkin
2023-03-31  3:38           ` Xuan Zhuo
2023-03-31  3:38             ` Xuan Zhuo
2021-05-26  8:24 ` [PATCH v3 4/4] virtio_net: disable cb aggressively Michael S. Tsirkin
2021-05-26  8:24   ` Michael S. Tsirkin
2021-05-26 15:15   ` Eric Dumazet
2021-05-26 15:15     ` Eric Dumazet
2021-05-26 21:22     ` Willem de Bruijn
2021-05-26 21:22       ` Willem de Bruijn
2021-05-26 19:39   ` Jakub Kicinski
2021-05-27  4:09   ` Jason Wang
2021-05-27  4:09     ` Jason Wang
2023-01-16 13:41   ` Laurent Vivier
2023-01-16 13:41     ` Laurent Vivier
2023-01-17  3:48     ` Jason Wang
2023-01-17  3:48       ` Jason Wang
2021-05-26 15:34 ` [PATCH v3 0/4] virtio net: spurious interrupt related fixes Willem de Bruijn
2021-05-26 15:34   ` Willem de Bruijn
2021-06-01  2:53   ` Willem de Bruijn
2021-06-01  2:53     ` Willem de Bruijn
2021-06-09 21:36     ` Willem de Bruijn
2021-06-09 21:36       ` Willem de Bruijn
2021-06-09 22:59       ` Willem de Bruijn
2021-06-09 22:59         ` Willem de Bruijn

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