linux-kernel - Re: dm-crypt parallelization patches

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Date:	Tue, 9 Apr 2013 14:08:06 -0400 (EDT)
From:	Mikulas Patocka <mpatocka@...hat.com>
To:	Tejun Heo <tj@...nel.org>
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, 9 Apr 2013, Tejun Heo wrote:

> On Tue, Apr 09, 2013 at 01:51:43PM -0400, Mikulas Patocka wrote:
> > The patch dm-crypt-sort-requests.patch sorts write requests submitted by a 
> > single thread. The requests are sorted according to the sector number, 
> > rb-tree is used for efficient sorting.
> 
> Hmmm? Why not just keep the issuing order along with plugging
> boundaries?

What do you mean?

I used to have a patch that keeps order of requests as they were 
introduced, but sorting the requests according to sector number is a bit 
simpler.

> > So it seems that CFQ has some deficiency that it cannot merge adjacent 
> > requests done by different processes.
> 
> As I wrote before, please use bio_associate_current().  Currently,
> dm-crypt is completely messing up all the context information that cfq
> depends on to schedule IOs.  Of course, it doesn't perform well.

bio_associate_current() is only valid on a system with cgroups and there 
are no cgroups on the kernel where I tested it. It is an empty function:

static inline int bio_associate_current(struct bio *bio) { return -ENOENT; }

Mikulas

> Thanks.
> 
> -- 
> tejun
> 
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