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    SubjectRe: [PATCH v3 2/4] virtio_net: move txq wakeups under tx q lock
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    在 2021/5/26 下午4:24, Michael S. Tsirkin 写道:
    > 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>


    Acked-by: Jason Wang <jasowang@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;
    > }
    >

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