linux-kernel - Re: [RESEND] [PATCH] readahead:add blk_run_backing

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Date:	Fri, 10 Jul 2009 13:27:29 +0400
From:	Vladislav Bolkhovitin <vst@...b.net>
To:	Ronald Moesbergen <intercommit@...il.com>
CC:	fengguang.wu@...el.com, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, kosaki.motohiro@...fujitsu.com,
	Alan.Brunelle@...com, hifumi.hisashi@....ntt.co.jp,
	linux-fsdevel@...r.kernel.org, jens.axboe@...cle.com,
	randy.dunlap@...cle.com, Bart Van Assche <bart.vanassche@...il.com>
Subject: Re: [RESEND] [PATCH] readahead:add blk_run_backing_dev


Vladislav Bolkhovitin, on 07/10/2009 12:43 PM wrote:
> Ronald Moesbergen, on 07/10/2009 10:32 AM wrote:
>>> I've also long ago noticed that reading data from block devices is slower
>>> than from files from mounted on those block devices file systems. Can
>>> anybody explain it?
>>>
>>> Looks like this is strangeness #2 which we uncovered in our tests (the first
>>> one was earlier in this thread why the context RA doesn't work with
>>> cooperative I/O threads as good as it should).
>>>
>>> Can you rerun the same 11 tests over a file on the file system, please?
>> I'll see what I can do. Just te be sure: you want me to run
>> blockdev-perftest on a file on the OCFS2 filesystem which is mounted
>> on the client over iScsi, right?
> 
> Yes, please.

Forgot to mention that you should also configure your backend storage as 
a big file on a file system (preferably, XFS) too, not as direct device, 
like /dev/vg/db-master.

Thanks,
Vlad

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