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Tsirkin" , linux-kernel@vger.kernel.org Cc: Jakub Kicinski , Wei Wang , David Miller , netdev@vger.kernel.org, Willem de Bruijn , virtualization@lists.linux-foundation.org References: <20210526082423.47837-1-mst@redhat.com> <20210526082423.47837-3-mst@redhat.com> From: Jason Wang Message-ID: <30c69182-cc6c-3e45-1db9-5b061e43e1d6@redhat.com> Date: Thu, 27 May 2021 11:48:33 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.10.2 MIME-Version: 1.0 In-Reply-To: <20210526082423.47837-3-mst@redhat.com> Content-Type: text/plain; charset=gbk; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ÔÚ 2021/5/26 ÏÂÎç4:24, Michael S. Tsirkin дµÀ: > 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 Acked-by: Jason Wang > --- > 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; > } >