>From f582caf612b446e42f1e80d5ef12c5b7322efd03 Mon Sep 17 00:00:00 2001 From: Dor Laor Date: Mon, 28 Jan 2008 02:09:48 +0200 Subject: [PATCH] virtio_net tx performance fix There was a problem with the location of the notify call in add_buff function: When VRING_USED_F_NO_NOTIFY is set, the host does not kick the guest when packets were transmited, as a result the guest runs out of tx buffers sometimes. This is fine but the problem lies when add_buf fails, it called notify and the host sends all the pending tx pkts. When enable_cb was called, more_used(vq) returned false so eventually the skb was droped. Moving notify from add_buf to enable_cb fixes this flow problem. The tx performance boosted from 220Mbps to 850Mbps. Signed-off-by: Dor Laor --- drivers/virtio/virtio_ring.c | 3 +-- 1 files changed, 1 insertions(+), 2 deletions(-) diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c index 3a28c13..592bbc9 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c @@ -87,8 +87,6 @@ static int vring_add_buf(struct virtqueue *_vq, if (vq->num_free < out + in) { pr_debug("Can't add buf len %i - avail = %i\n", out + in, vq->num_free); - /* We notify *even if* VRING_USED_F_NO_NOTIFY is set here. */ - vq->notify(&vq->vq); END_USE(vq); return -ENOSPC; } @@ -232,6 +230,7 @@ static bool vring_enable_cb(struct virtqueue *_vq) vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT; mb(); if (unlikely(more_used(vq))) { + vq->notify(&vq->vq); vq->vring.avail->flags |= VRING_AVAIL_F_NO_INTERRUPT; END_USE(vq); return false; -- 1.5.3.7