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@xxxxxxxxxx>
---
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
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