linux-kernel - Re: dm-crypt parallelization patches

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Date:	Tue, 9 Apr 2013 12:52:59 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Mikulas Patocka <mpatocka@...hat.com>
Cc:	Jens Axboe <axboe@...nel.dk>, Vivek Goyal <vgoyal@...hat.com>,
	Mike Snitzer <snitzer@...hat.com>,
	Milan Broz <gmazyland@...il.com>, dm-devel@...hat.com,
	Andi Kleen <andi@...stfloor.org>, dm-crypt@...ut.de,
	linux-kernel@...r.kernel.org,
	Christoph Hellwig <hch@...radead.org>,
	Christian Schmidt <schmidt@...add.de>
Subject: Re: dm-crypt parallelization patches

On Tue, Apr 09, 2013 at 03:42:16PM -0400, Mikulas Patocka wrote:
> If I drop ifdefs, it doesn't compile (because other cgroup stuff it 
> missing).
> 
> So I enabled bio cgroups.
> 
> bio_associate_current can't be used, because by the time we allocate the 
> outgoing write bio, we are no longer in the process that submitted the 
> original bio.

Oh, I suppose it'd need some massaging to selectively turn off the
cgroup part.

> Anyway, I tried to reproduce in dm-crypt what bio_associate_current does - 

and we probably need to change that to bio_associate_task().

> in the submitting process I record "ioc" and "css" fields in "dm_crypt_io" 
> structure and set these fields on all outgoing bios. It has no effect on 
> performance, it is as bad as if I hadn't done it.

A good way to verify that the tagging is correct would be configuring
io limits in block cgroup and see whether the limits are correctly
applied when going through dm-crypt (please test with direct-io or
reads, writeback is horribly broken, sorry).working correctly, maybe
plugging is the overriding factor?

Thanks.

-- 
tejun
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