netdev - Re: [PATCH] tcp: allow splice() to build full TSO packets

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Date:	Thu, 05 Apr 2012 19:05:09 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	netdev@...r.kernel.org, ncardwell@...gle.com, therbert@...gle.com,
	ycheng@...gle.com, hkchu@...gle.com, maze@...gle.com,
	maheshb@...gle.com, ilpo.jarvinen@...sinki.fi, nanditad@...gle.com
Subject: Re: [PATCH] tcp: allow splice() to build full TSO packets

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Thu, 05 Apr 2012 15:05:35 +0200

> Hmm, thinking again about this, I did more tests and it appears we need
> to differentiate the SPLICE_F_MORE flag (user request) and the internal
> marker provided by splice logic (handling a batch of pages)
> 
> A program doing splice(... SPLICE_F_MORE) should really call tcp_push()
> at the end of its work.

This is the kind of problem I was hoping we weren't introducing
when I asked about sendfile() et al. the other day :-)

> [PATCH] tcp: tcp_sendpages() should call tcp_push() once
> 
> commit 2f533844242 (tcp: allow splice() to build full TSO packets) added
> a regression for splice() calls using SPLICE_F_MORE.
> 
> We need to call tcp_flush() at the end of the last page processed in
> tcp_sendpages(), or else transmits can be deferred and future sends
> stall.
> 
> Add a new internal flag, MSG_SENDPAGE_NOTLAST, acting like MSG_MORE, but
> with different semantic.
> 
> For all sendpage() providers, its a transparent change. Only
> sock_sendpage() and tcp_sendpages() can differentiate the two different
> flags provided by pipe_to_sendpage()
> 
> Reported-by: Tom Herbert <therbert@...gle.com>
> Cc: Nandita Dukkipati <nanditad@...gle.com>
> Cc: Neal Cardwell <ncardwell@...gle.com>
> Cc: Tom Herbert <therbert@...gle.com>
> Cc: Yuchung Cheng <ycheng@...gle.com>
> Cc: H.K. Jerry Chu <hkchu@...gle.com>
> Cc: Maciej Żenczykowski <maze@...gle.com>
> Cc: Mahesh Bandewar <maheshb@...gle.com>
> Cc: Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>
> Signed-off-by: Eric Dumazet <eric.dumazet@...il>com>

Applied, thanks Eric.
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