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@xxxxxxxxxx>
---
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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