linux-kernel - Re: request baset device mapper in Linux

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Date:	Wed, 5 Oct 2011 12:35:45 +0200
From:	Lukas Hejtmanek <xhejtman@....muni.cz>
To:	"Jun'ichi Nomura" <j-nomura@...jp.nec.com>
Cc:	Mike Snitzer <snitzer@...hat.com>,
	Kiyoshi Ueda <k-ueda@...jp.nec.com>, agk@...hat.com,
	linux-kernel@...r.kernel.org
Subject: Re: request baset device mapper in Linux

On Wed, Oct 05, 2011 at 05:13:36PM +0900, Jun'ichi Nomura wrote:
> > yes, 3GB/s and only kwapd0 and kswapd1 is running, no kworker or ksoftirqd..
> 
> Hmm.. did you find any difference in your profile this time?

not sure what do you mean.

> I'm trying to reproduce it myself but no success so far
> (perhaps disks are not fast enough to saturate CPU on my test machine).

hmm, I have 80 SAS 2.0 disks and two E5640 @ 2.67GHz cpus. 
 
> As ksoftirqd in top implies your CPU4 gets too much I/O completions,
> 'rq_affnity = 2' for both dm and SCSI devices might be a solution.
> It'll distribute block completion softirqs to submitters and possibly
> reduce the loads of the 1st CPU in the socket.
> (See the commit below. It's a new feature of 3.1. Not available in 3.0...)

So what next? Should I try 3.1 kernel with this patch applied?

-- 
Lukáš Hejtmánek
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