linux-kernel - Re: [-RT] multiple streams have degraded performance

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Message-Id: <1182235898.7348.361.camel@twins>
Date:	Tue, 19 Jun 2007 08:51:38 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vernon Mauery <vernux@...ibm.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>, Jeff Garzik <jeff@...zik.org>
Subject: Re: [-RT] multiple streams have degraded performance

On Mon, 2007-06-18 at 22:12 -0700, Vernon Mauery wrote:
> In looking at the performance characteristics of my network I found that 
> 2.6.21.5-rt15 suffers from degraded thoughput with multiple threads.  The 
> test that I did this with is simply invoking 1, 2, 4, and 8 instances of 
> netperf at a time and measuring the total throughput.  I have two 4-way 
> machines connected with 10GbE cards.  I tested several kernels (some older 
> and some newer) and found that the only thing in common was that with -RT 
> kernels the performance went down with concurrent streams.
> 
> While the test was showing the numbers for receiving as well as sending, the 
> receiving numbers are not reliable because that machine was running a -RT 
> kernel for these tests.
> 
> I was just wondering if anyone had seen this problem before or would have any 
> idea on where to start hunting for the solution.

could you enable CONFIG_LOCK_STAT

echo 0 > /proc/lock_stat

<run your test>

and report the output of (preferably not 80 column wrapped):

grep : /proc/lock_stat | head

or otherwise if there are any highly contended network locks listed?

 - Peter

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