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Date: Wed, 09 Mar 2011 11:21:53 +0100
From: Milan Broz <mbroz@redhat.com>
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Subject: Re: [dm-crypt] Slow I/O with LUKS on amd64
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To: Thomas Damgaard <thomasdn@gmail.com>
Cc: dm-crypt@saout.de

On 03/09/2011 09:11 AM, Thomas Damgaard wrote:
> I have recently switched from i386 to amd64. After switching to 64
> bit, I/O on LUKS encrypted devices became horribly slow.
> Do you have any idea what causes this? Or suggestions on how to debug
> this further?
> 
> I have submitted a bug report on this on Launchpad. The report
> includes details on performance, hardware, etc.

Well, seems you already proved the it is Ubuntu kernel only problem.

So generic suggestions - be sure that

- you are always using the same encryption parameters (cipher, key size)
(once device is unlocked, performance is kernel only thing, so this cannot
be cryptsetup/LUKS problem)

- if you are testing fs over dmcrypt, be sure the same fs with the *same*
mount parameters is used. If using barriers switch them off for test.
(barrier=0). Verify with dmesg log.

- check which kernel cryptoAPI module is used for the encryption
(kernel should load arch sepcific one, e.g. aes_x86_64 vs aes_i586, not
generic one). usually simple lsmod of loaded modules here gives you hint.
Try blacklist that module so generic one is used etc.

- try some new kernel, I think even Ubuntu provides upstream snapshots

There is no reason x86_64 should be slower - many people it using, even on the
same hw you have.

Milan