>From f582caf612b446e42f1e80d5ef12c5b7322efd03 Mon Sep 17 00:00:00 2001
From: Dor Laor <dor.laor@xxxxxxxxxxxx>
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 transmitted, 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 dropped.
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 <dor.laor@xxxxxxxxxxxx>
---
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
Attachment:
0001-virtio_net-tx-performance-fix.patch
Description: application/mbox
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