linux-kernel - Re: rq_affinity doesn't seem to work?

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Message-ID: <20110713171011.GA11864@parisc-linux.org>
Date:	Wed, 13 Jul 2011 11:10:11 -0600
From:	Matthew Wilcox <matthew@....cx>
To:	Jens Axboe <axboe@...nel.dk>
Cc:	"Jiang, Dave" <dave.jiang@...el.com>,
	"Williams, Dan J" <dan.j.williams@...el.com>,
	"Foong, Annie" <annie.foong@...el.com>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Nadolski, Edmund" <edmund.nadolski@...el.com>,
	"Skirvin, Jeffrey D" <jeffrey.d.skirvin@...el.com>
Subject: Re: rq_affinity doesn't seem to work?

On Tue, Jul 12, 2011 at 10:30:35PM +0200, Jens Axboe wrote:
> It's probably the grouping, we need to do something about that. Does the
> below patch make it behave as you expect?

"something", absolutely.  But there is benefit from doing some aggregation
(we tried disabling it entirely with the "well-known OLTP benchmark" and
performance went down).

Ideally we'd do something like "if the softirq is taking up more than 10%
of a core, split the grouping".  Do we have enough stats to do that kind
of monitoring?

-- 
Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."
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