On (Sat) Aug 22 2009 [17:31:26], Rusty Russell wrote:
> On Wed, 19 Aug 2009 01:31:29 am Amit Shah wrote:
> > This helper returns 1 if a call to add_buf will not fail
> > with -ENOSPC.
> >
> > This will help callers that do
> >
> > while(1) {
> > alloc()
> > if (add_buf()) {
> > free();
> > break;
> > }
> > }
> >
> > This will result in one less alloc/free exercise.
>
> Hi Amit,
>
> This is what I have in my tree; similar motivation. I didn't
> adapt virtio_net like you did tho.
Hi Rusty,
This works too. A simple (untested) patch to make virtio_net use it:
>From a252db16c737b608efffcec22cade1c914dfe859 Mon Sep 17 00:00:00 2001
From: Amit Shah <amit.shah@xxxxxxxxxx>
Date: Mon, 24 Aug 2009 13:07:04 +0530
Subject: [PATCH] virtio_net: Check for room in the vq before adding buffer
Saves us one cycle of alloc-add-free if the queue
was full.
Signed-off-by: Amit Shah <amit.shah@xxxxxxxxxx>
---
drivers/net/virtio_net.c | 18 ++++++++++--------
1 files changed, 10 insertions(+), 8 deletions(-)
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index e94f817..1f45a10 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -276,11 +276,12 @@ static bool try_fill_recv_maxbufs(struct virtnet_info *vi, gfp_t gfp)
{
struct sk_buff *skb;
struct scatterlist sg[2+MAX_SKB_FRAGS];
- int num, err, i;
+ int num, ret, i;
bool oom = false;
sg_init_table(sg, 2+MAX_SKB_FRAGS);
- for (;;) {
+ ret = 1;
+ while(ret > 0) { /* Is there space to add another buffer to the vq */
struct skb_vnet_hdr *hdr;
skb = netdev_alloc_skb(vi->dev, MAX_PACKET_LEN + NET_IP_ALIGN);
@@ -315,8 +316,8 @@ static bool try_fill_recv_maxbufs(struct virtnet_info *vi, gfp_t gfp)
num = skb_to_sgvec(skb, sg+1, 0, skb->len) + 1;
skb_queue_head(&vi->recv, skb);
- err = vi->rvq->vq_ops->add_buf(vi->rvq, sg, 0, num, skb);
- if (err < 0) {
+ ret = vi->rvq->vq_ops->add_buf(vi->rvq, sg, 0, num, skb);
+ if (ret < 0) {
skb_unlink(skb, &vi->recv);
trim_pages(vi, skb);
kfree_skb(skb);
@@ -335,13 +336,14 @@ static bool try_fill_recv(struct virtnet_info *vi, gfp_t gfp)
{
struct sk_buff *skb;
struct scatterlist sg[1];
- int err;
+ int ret;
bool oom = false;
if (!vi->mergeable_rx_bufs)
return try_fill_recv_maxbufs(vi, gfp);
- for (;;) {
+ ret = 1;
+ while(ret > 0) { /* Is there space to add another buffer to the vq */
skb_frag_t *f;
skb = netdev_alloc_skb(vi->dev, GOOD_COPY_LEN + NET_IP_ALIGN);
@@ -368,8 +370,8 @@ static bool try_fill_recv(struct virtnet_info *vi, gfp_t gfp)
sg_init_one(sg, page_address(f->page), PAGE_SIZE);
skb_queue_head(&vi->recv, skb);
- err = vi->rvq->vq_ops->add_buf(vi->rvq, sg, 0, 1, skb);
- if (err < 0) {
+ ret = vi->rvq->vq_ops->add_buf(vi->rvq, sg, 0, 1, skb);
+ if (ret < 0) {
skb_unlink(skb, &vi->recv);
kfree_skb(skb);
break;
--
1.6.2.5
Amit
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