Re: Major network performance regression in 3.7

Willy Tarreau
2013-01-06T17:35:43Z

On Sun, Jan 06, 2013 at 09:10:55AM -0800, Eric Dumazet wrote:
> On Sun, 2013-01-06 at 17:44 +0100, Willy Tarreau wrote:
> > On Sun, Jan 06, 2013 at 08:39:53AM -0800, Eric Dumazet wrote:
> > > Hmm, I'll have to check if this really can be reverted without hurting
> > > vmsplice() again.
> >
> > Looking at the code I've been wondering whether we shouldn't transform
> > the condition to perform the push if we can't push more segments, but
> > I don't know what to rely on. It would be something like this :
> >
> > if (copied &&
> > (!(flags & MSG_SENDPAGE_NOTLAST) || cant_push_more))
> > tcp_push(sk, flags, mss_now, tp->nonagle);
>
> Good point !
>
> Maybe the following fix then ?
>
>
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index 1ca2536..7ba0717 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -941,8 +941,10 @@ out:
> return copied;
>
> do_error:
> - if (copied)
> + if (copied) {
> + flags &= ~MSG_SENDPAGE_NOTLAST;
> goto out;
> + }
> out_err:
> return sk_stream_error(sk, flags, err);
> }

Unfortunately it does not work any better, which means to me
that we don't leave via this code path. I tried other tricks
which failed too. I need to understand this part better before
randomly fiddling with it.

Willy