Re: Major network performance regression in 3.7

Willy Tarreau
2013-01-06T02:18:30Z

On Sat, Jan 05, 2013 at 06:16:31PM -0800, Eric Dumazet wrote:
> On Sat, 2013-01-05 at 17:51 -0800, Eric Dumazet wrote:
> > On Sat, 2013-01-05 at 17:40 -0800, Eric Dumazet wrote:
> > > On Sun, 2013-01-06 at 02:30 +0100, Willy Tarreau wrote:
> > >
> > > > Ah interesting because these were some of the mm patches that I had
> > > > tried to revert.
> > >
> > > Hmm, or we should fix __skb_splice_bits()
> > >
> > > I'll send a patch.
> > >
> >
> > Could you try the following ?
>
> Or more exactly...

The first one did not change a iota unfortunately. I'm about to
spot the commit causing the loopback regression. It's a few patches
before the first one you pointed. It's almost finished and I test
your patch below immediately after.

Thanks,
Willy

> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 3ab989b..01f222c 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -1736,11 +1736,8 @@ static bool __splice_segment(struct page *page, unsigned int poff,
> return false;
> }
>
> - /* ignore any bits we already processed */
> - if (*off) {
> - __segment_seek(&page, &poff, &plen, *off);
> - *off = 0;
> - }
> + __segment_seek(&page, &poff, &plen, *off);
> + *off = 0;
>
> do {
> unsigned int flen = min(*len, plen);
> @@ -1768,14 +1765,15 @@ static bool __skb_splice_bits(struct sk_buff *skb, struct pipe_inode_info *pipe,
> struct splice_pipe_desc *spd, struct sock *sk)
> {
> int seg;
> + struct page *page = virt_to_page(skb->data);
> + unsigned int poff = skb->data - (unsigned char *)page_address(page);
>
> /* map the linear part :
> * If skb->head_frag is set, this 'linear' part is backed by a
> * fragment, and if the head is not shared with any clones then
> * we can avoid a copy since we own the head portion of this page.
> */
> - if (__splice_segment(virt_to_page(skb->data),
> - (unsigned long) skb->data & (PAGE_SIZE - 1),
> + if (__splice_segment(page, poff,
> skb_headlen(skb),
> offset, len, skb, spd,
> skb_head_is_locked(skb),
>