linux-kernel - Re: Performance regression in IO scheduler still there

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Date:	Fri, 06 Nov 2009 09:14:53 -0500
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Corrado Zoccolo <czoccolo@...il.com>
Cc:	Jan Kara <jack@...e.cz>, jens.axboe@...cle.com,
	LKML <linux-kernel@...r.kernel.org>,
	Chris Mason <chris.mason@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mike Galbraith <efault@....de>
Subject: Re: Performance regression in IO scheduler still there

Corrado Zoccolo <czoccolo@...il.com> writes:

> Hi Jeff,
> what hardware are you using for tests?
> I see aggregated random read bandwidth is larger than sequential read
> bandwidth, and write bandwidth greater than read.
> Is this a SAN with multiple independent spindles?

Yeah, this is a single path to an HP EVA storage array.  There are 24 or
so disks striped in the pool used to create the volume I am using.  Jan,
could you repeat your tests with /sys/block/sdX/queue/iosched/low_latency
set to 0?

Cheers,
Jeff
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