netdev - Re: Loopback and Nagle's algorithm

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Message-ID: <1302613703.3233.40.camel@edumazet-laptop>
Date:	Tue, 12 Apr 2011 15:08:23 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jiri Kosina <jkosina@...e.cz>
Cc:	Adam McLaurin <lkml@...tas.net>,
	Will Newton <will.newton@...il.com>,
	linux-kernel@...r.kernel.org, netdev <netdev@...r.kernel.org>
Subject: Re: Loopback and Nagle's algorithm

Le mardi 12 avril 2011 à 13:54 +0200, Jiri Kosina a écrit :
> On Tue, 12 Apr 2011, Adam McLaurin wrote:
> 
> > > It may be caused by an increase in context switch rate, as both sender
> > > and receiver are on the same machine.
> > 
> > I'm not sure that's what's happening, since the box where I'm running
> > this test has 8 physical CPU's and 32 cores in total.
> 
> Have you tried firing up the testcase under perf, to see what it reveals 
> as the bottleneck?
> 
CC netdev

This rings a bell here.

I suspect we hit mod_timer() / lock_timer_base()  because of delack
timer constantly changing.

I remember raising this point last year :

http://kerneltrap.org/mailarchive/linux-netdev/2010/5/20/6277741

David answer : 
http://kerneltrap.org/mailarchive/linux-netdev/2010/6/2/6278430

I am afraid no change was done...


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