Re: [PATCHv2 RFC 3/4] virtio_net: limit xmit polling
From: "Michael S. Tsirkin" <mst@redhat.com>
Date: 2011-06-07 15:59:15
Subsystem:
networking drivers, the rest, virtio net driver · Maintainers:
Andrew Lunn, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds, "Michael S. Tsirkin", Jason Wang, Eugenio Pérez
Possibly related (same subject, not in this thread)
- 2011-06-02 · Re: [PATCHv2 RFC 3/4] virtio_net: limit xmit polling · "Michael S. Tsirkin" <mst@redhat.com>
- 2011-06-02 · Re: [PATCHv2 RFC 3/4] virtio_net: limit xmit polling · Sridhar Samudrala <hidden>
- 2011-06-02 · [PATCHv2 RFC 3/4] virtio_net: limit xmit polling · "Michael S. Tsirkin" <mst@redhat.com>
On Thu, Jun 02, 2011 at 06:43:17PM +0300, Michael S. Tsirkin wrote:
Current code might introduce a lot of latency variation if there are many pending bufs at the time we attempt to transmit a new one. This is bad for real-time applications and can't be good for TCP either. Free up just enough to both clean up all buffers eventually and to be able to xmit the next packet. Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
I've been testing this patch and it seems to work fine so far. The following fixups are needed to make it build though:
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index b25db1c..77cdf34 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c@@ -529,11 +529,8 @@ static bool free_old_xmit_skb(struct virtnet_info *vi) * virtqueue_add_buf will succeed. */ static bool free_xmit_capacity(struct virtnet_info *vi) { - struct sk_buff *skb; - unsigned int len; - while (virtqueue_min_capacity(vi->svq) < MAX_SKB_FRAGS + 2) - if (unlikely(!free_old_xmit_skb)) + if (unlikely(!free_old_xmit_skb(vi))) return false; return true; }
@@ -628,7 +625,7 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev) * Doing this after kick means there's a chance we'll free * the skb we have just sent, which is hot in cache. */ for (i = 0; i < 2; i++) - free_old_xmit_skb(v); + free_old_xmit_skb(vi); if (likely(free_xmit_capacity(vi))) return NETDEV_TX_OK;