netdev - Re: Stable regression with 'tcp: allow splice() to build full TSO packets'

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Date:	Thu, 17 May 2012 23:50:10 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Willy Tarreau <w@....eu>
Cc:	netdev@...r.kernel.org
Subject: Re: Stable regression with 'tcp: allow splice() to build full TSO
 packets'

On Thu, 2012-05-17 at 23:40 +0200, Eric Dumazet wrote:

> I dont understand why we should tcp_push() if we sent 0 bytes in this
> splice() call.
> 
> The push() should have be done already by prior splice() call, dont you
> think ?
> 
> out:
> 	if (copied && !(flags & MSG_SENDPAGE_NOTLAST))
> 		tcp_push(sk, flags, mss_now, tp->nonagle);
> 

I think I now understand

One splice() syscall actually calls do_tcp_sendpages() several times
(N).

Problem is N-1 calls are done with MSG_SENDPAGE_NOTLAST set

And last one with MSG_SENDPAGE_NOTLAST unset

So maybe we should replace this test by :

	if (!(flags & MSG_SENDPAGE_NOTLAST))
		tcp_push(...);



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