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Date: Tue, 24 Jul 2012 15:54:06 +0200
From: Milan Broz <mbroz@redhat.com>
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Subject: Re: [dm-crypt] aes-xts-plain with aes_x86_64 makes my SSD 5x slower
 than my encrypted HD
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To: Marc MERLIN <marc@merlins.org>
Cc: dm-crypt@saout.de, Yves-Alexis Perez <corsac@debian.org>

On 07/24/2012 07:57 AM, Marc MERLIN wrote:
> Mmmh, so I installed "standard" linux-image-3.2.0-3-amd64 from debian.
> And....
> nothing changed :(

Well. I found SSD where I can reproduce something similar.
Seems page cache messes something with readahead...


# lsblk /dev/sdc -t
NAME                    ALIGNMENT MIN-IO OPT-IO PHY-SEC LOG-SEC ROTA SCHED RQ-SIZE
sdc                             0    512      0     512     512    0 noop      128
└─sdc_null_crypt (dm-0)         0    512      0     512     512    0           128


- Disable readahead
# blockdev --setra 0 /dev/mapper/sdc_null_crypt 

# hdparm -t /dev/mapper/sdc_null_crypt 
 Timing buffered disk reads:  106 MB in  3.01 seconds =  35.18 MB/sec

(pretty bad)

But with direct-io it still works:
# hdparm --direct -t /dev/mapper/sdc_null_crypt 
 Timing O_DIRECT disk reads:  698 MB in  3.00 seconds = 232.44 MB/sec

(now with read-ahead set to 4M)

# blockdev --setra 8192 /dev/mapper/sdc_null_crypt 
# hdparm -t /dev/mapper/sdc_null_crypt 
 Timing buffered disk reads:  664 MB in  3.00 seconds = 221.29 MB/sec

So. Can you please try to increase readahead (and also run it with direct-io)?
Just to check if it is the same problem or not...

Thanks,
Milan