netdev - Re: Major network performance regression in 3.7

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Date:	Sun, 6 Jan 2013 22:52:00 +0100
From:	Willy Tarreau <w@....eu>
To:	John Stoffel <john@...ffel.org>
Cc:	Eric Dumazet <eric.dumazet@...il.com>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: Major network performance regression in 3.7

On Sun, Jan 06, 2013 at 04:49:35PM -0500, John Stoffel wrote:
> >>>>> "Willy" == Willy Tarreau <w@....eu> writes:
> 
> Willy> On Sun, Jan 06, 2013 at 11:00:15AM -0800, Eric Dumazet wrote:
> >> On Sun, 2013-01-06 at 10:51 -0800, Eric Dumazet wrote:
> >> > > 
> >> > > (sd->len is usually 4096, which is expected, but sd->total_len value is
> >> > > huge in your case, so we always set the flag in fs/splice.c)
> >> > 
> >> > I am testing :
> >> > 
> >> >        if (sd->len < sd->total_len && pipe->nrbufs > 1)
> >> >                 more |= MSG_SENDPAGE_NOTLAST;
> >> > 
> >> 
> >> Yes, this should fix the problem :
> >> 
> >> If there is no following buffer in the pipe, we should not set NOTLAST.
> >> 
> >> diff --git a/fs/splice.c b/fs/splice.c
> >> index 8890604..6909d89 100644
> >> --- a/fs/splice.c
> >> +++ b/fs/splice.c
> >> @@ -696,8 +696,10 @@ static int pipe_to_sendpage(struct pipe_inode_info *pipe,
> >> return -EINVAL;
> >> 
> >> more = (sd->flags & SPLICE_F_MORE) ? MSG_MORE : 0;
> >> -	if (sd->len < sd->total_len)
> >> +
> >> +	if (sd->len < sd->total_len && pipe->nrbufs > 1)
> >> more |= MSG_SENDPAGE_NOTLAST;
> >> +
> >> return file->f_op->sendpage(file, buf->page, buf->offset,
> sd-> len, &pos, more);
> >> }
>  
> Willy> OK it works like a charm here now ! I can't break it anymore, so it
> Willy> looks like you finally got it !
> 
> It's still broken, there's no comments in the code to explain all this
> magic to mere mortals!  *grin*

I would generally agree, but when Eric fixes such a thing, he
generally goes with lengthy details in the commit message.

Willy

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