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 <[email protected]> --- drivers/net/virtio_net.c | 18 +++++++++++------- 1 files changed, 11 insertions(+), 7 deletions(-) diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c index f33c92b..9982bd7 100644 --- a/drivers/net/virtio_net.c +++ b/drivers/net/virtio_net.c @@ -509,17 +509,23 @@ again: return received; } -static void free_old_xmit_skbs(struct virtnet_info *vi) +static bool free_old_xmit_skbs(struct virtnet_info *vi, int capacity) { struct sk_buff *skb; unsigned int len; + bool c; + /* We try to free up at least 2 skbs per one sent, so that we'll get + * all of the memory back if they are used fast enough. */ + int n = 2; - while ((skb = virtqueue_get_buf(vi->svq, &len)) != NULL) { + while ((c = virtqueue_get_capacity(vi->svq) >= capacity) && --n > 0 && + (skb = virtqueue_get_buf(vi->svq, &len)) != NULL) { pr_debug("Sent skb %p\n", skb); vi->dev->stats.tx_bytes += skb->len; vi->dev->stats.tx_packets++; dev_kfree_skb_any(skb); } + return c; } static int xmit_skb(struct virtnet_info *vi, struct sk_buff *skb) @@ -574,8 +580,8 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev) struct virtnet_info *vi = netdev_priv(dev); int capacity; - /* Free up any pending old buffers before queueing new ones. */ - free_old_xmit_skbs(vi); + /* Free enough pending old buffers to enable queueing new ones. */ + free_old_xmit_skbs(vi, 2+MAX_SKB_FRAGS); /* Try to transmit */ capacity = xmit_skb(vi, skb); @@ -609,9 +615,7 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev) netif_stop_queue(dev); if (unlikely(!virtqueue_enable_cb_delayed(vi->svq))) { /* More just got used, free them then recheck. */ - free_old_xmit_skbs(vi); - capacity = virtqueue_get_capacity(vi->svq); - if (capacity >= 2+MAX_SKB_FRAGS) { + if (!likely(free_old_xmit_skbs(vi, 2+MAX_SKB_FRAGS))) { netif_start_queue(dev); virtqueue_disable_cb(vi->svq); } -- 1.7.5.53.gc233e -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
