linux-kernel - Re: direct-io regression [Was: How to track down abysmal performance ata - raid1 - crypto - vg/lv

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Message-ID: <20100805163519.GA6604@comet.dominikbrodowski.net>
Date:	Thu, 5 Aug 2010 18:35:19 +0200
From:	Dominik Brodowski <linux@...inikbrodowski.net>
To:	Chris Mason <chris.mason@...cle.com>, josef@...hat.com,
	Valdis.Kletnieks@...edu,
	Michael Monnerie <michael.monnerie@...it-management.at>,
	Christoph Hellwig <hch@...radead.org>,
	linux-raid@...r.kernel.org, xfs@....sgi.com,
	linux-kernel@...r.kernel.org, dm-devel@...hat.com
Subject: Re: direct-io regression [Was: How to track down abysmal
 performance ata - raid1 - crypto - vg/lv - xfs]

Small correction:

On Thu, Aug 05, 2010 at 05:35:19PM +0200, Dominik Brodowski wrote:
> With this fix, I get proper speeds when doing dio reads from
> /dev/mapper/vg0-*_crypt; see the 17.3 MB/s above. Most strangely,
> also accesing /dev/mapper/vg0-* (un-encrypted) and the raw
> device at /dev/sda* speeds up (to up to 28 MB/s). Was only seeing around
> 16 to 18 MB/s without this patch for unencrypted access.

The speed-up of the unencrypted access (18 -> 28 MB/s) is caused by using a
different configuration for kernel 2.6.35; and seems to be unrelated to your
patch. Will try to track down which config option is the culprit.


kernel, dmcrypt?	| good config | bad config
-------------------------------------------------
patched 2.6.35, dmcrypt	  ~ 18 MB/s	~ 13 MB/s
patched 2.6.35		  ~ 28 MB/s	~ 18 MB/s
-------------------------------------------------
plain 2.6.35, dmcrypt	  ~  3 MB/s	~  3 MB/s
plain 2.6.35		  <not tested>	~ 16 MB/s	


Best,
	Dominik
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