[PATCH RFC v3 3/3] virtio-net: optimize free_old_xmit_skbs stats

From: Michael S. Tsirkin
Date: Mon Oct 20 2014 - 02:49:18 EST


From: Jason Wang <jasowang@xxxxxxxxxx>

We already have counters for sent packets and sent bytes.
Use them to reduce the number of u64_stats_update_begin/end().

Take care not to bother with stats update when called
speculatively.

Based on a patch by Jason Wang.

Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
---
drivers/net/virtio_net.c | 16 +++++++++++-----
1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index b83d39d..c2b69f8 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -233,16 +233,22 @@ static unsigned int free_old_xmit_skbs(struct netdev_queue *txq,
(skb = virtqueue_get_buf(sq->vq, &len)) != NULL) {
pr_debug("Sent skb %p\n", skb);

- u64_stats_update_begin(&stats->tx_syncp);
- stats->tx_bytes += skb->len;
bytes += skb->len;
- stats->tx_packets++;
- u64_stats_update_end(&stats->tx_syncp);
+ packets++;

dev_kfree_skb_any(skb);
- packets++;
}

+ /* Avoid overhead when no packets have been processed
+ * happens when called speculatively from start_xmit. */
+ if (!packets)
+ return 0;
+
+ u64_stats_update_begin(&stats->tx_syncp);
+ stats->tx_bytes += bytes;
+ stats->tx_packets += packets;
+ u64_stats_update_end(&stats->tx_syncp);
+
netdev_tx_completed_queue(txq, packets, bytes);

if (sq->vq->num_free >= 2+MAX_SKB_FRAGS)
--
MST

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/