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Re: direct-io regression [Was: How to track down abysmal performance ata

To: Chris Mason <chris.mason@xxxxxxxxxx>, josef@xxxxxxxxxx, Valdis.Kletnieks@xxxxxx, Michael Monnerie <michael.monnerie@xxxxxxxxxxxxxxxxxxx>, Christoph Hellwig <hch@xxxxxxxxxxxxx>, linux-raid@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, dm-devel@xxxxxxxxxx
Subject: Re: direct-io regression [Was: How to track down abysmal performance ata - raid1 - crypto - vg/lv - xfs]
From: Dominik Brodowski <linux@xxxxxxxxxxxxxxxxxxxx>
Date: Thu, 5 Aug 2010 18:35:19 +0200
In-reply-to: <20100805153519.GA7242@xxxxxxxxxxxxxxxxxxxxxxxxxx>
Mail-followup-to: Dominik Brodowski <linux@xxxxxxxxxxxxxxxxxxxx>, Chris Mason <chris.mason@xxxxxxxxxx>, josef@xxxxxxxxxx, Valdis.Kletnieks@xxxxxx, Michael Monnerie <michael.monnerie@xxxxxxxxxxxxxxxxxxx>, Christoph Hellwig <hch@xxxxxxxxxxxxx>, linux-raid@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, dm-devel@xxxxxxxxxx
References: <20100805123649.GA18672@xxxxxxxxxxxxxxxxxxxxxxxxxx> <20100805113240.GA29846@think> <20100805153519.GA7242@xxxxxxxxxxxxxxxxxxxxxxxxxx>
User-agent: Mutt/1.5.20 (2009-06-14)
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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