netdev - Re: [PATCH] tcp: disable auto corking by default

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Message-ID: <20140208165539.GA22359@glanzmann.de>
Date:	Sat, 8 Feb 2014 17:55:39 +0100
From:	Thomas Glanzmann <thomas@...nzmann.de>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Eric Dumazet <edumazet@...gle.com>,
	"David S. Miller" <davem@...emloft.net>,
	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>,
	target-devel <target-devel@...r.kernel.org>,
	Linux Network Development <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tcp: disable auto corking by default

Hello Eric,

> > Disable auto corking by default

> We should let auto corking on during 3.14 development cycle so that we
> can fix the bugs, and thing of some optimizations.

I agree that leaving it enabled helps to find bugs, however I'm not
happy with the round trip time degradation.

> auto cork gives a strong incentive to applications to use
> TCP_CORK/MSG_MORE to avoid overhead of sending multiple small
> segments.

I agree. But if it breaks the application many people won't be happy,
for example I spend already 5 hours to track it down.

> In the normal case, the extra delay is something like 10 us, so if an
> application is really hit by this delay, its a strong sign it could be
> improved, especially if auto corking is off.

Yes, but 230 micro seconds for others. :-(

> Lets wait the end of 3.14 dev cycle before considering this patch.

I agree.

Btw. I mixed up the pcaps for autocork on and off, so I moved the files
that they know show what they should show.

Cheers,
        Thomas
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