linux-kernel - Re: dm-crypt: Performance Regression 2.6.37 -> 2.6.38-rc8

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Date:	Thu, 10 Mar 2011 18:54:12 +0100
From:	"Mario 'BitKoenig' Holbe" <Mario.Holbe@...Ilmenau.DE>
To:	Andi Kleen <ak@...ux.intel.com>
Cc:	dm-crypt@...ut.de, linux-kernel@...r.kernel.org,
	Milan Broz <mbroz@...hat.com>,
	Alasdair G Kergon <agk@...hat.com>
Subject: Re: dm-crypt: Performance Regression 2.6.37 -> 2.6.38-rc8

On Thu, Mar 10, 2011 at 08:57:30AM -0800, Andi Kleen wrote:
> On Tue, Mar 08, 2011 at 05:45:08PM +0100, Mario 'BitKoenig' Holbe wrote:
> > I'm running a 4-disk RAID0 on top of 4 independent dm-crypt(aes-xts)
> > devices on a Core2Quad 3GHz. This setup did overcome the single-CPU
> Do you actually use dd for production or is this just a benchmark?

The array is streaming most of the time, i.e. single-process sequential
read or write (read mostly) for large chunks of data.
So, no and yes, but...

> (if yes: newsflash: use a better benchmark)

this makes dd quite a valid benchmark for me in this case.

> It will be better with multiple processes running on different CPUs. 
> The new design is really for multiple processes.

Of course it is. What bother me is that I can't get back my old
performance in my case whatever I do.

I don't know what kind of parallelism padata uses, i.e. whether a
padata-based solution would suffer from the same limitations like the
current dm-crypt/kcryptd-parallelism or not.

Wth the current approach:
Would it be possible to make CPU-affinity configurable for *single*
kcryptd instances? Either in the way to nail a specific kcryptd to a
specific CPU or (what would be better for me, I guess) in the way to
completely remove CPU-affinity from a specific kcryptd, like it was
before?

Mario
-- 
There is nothing more deceptive than an obvious fact.
             -- Sherlock Holmes by Arthur Conan Doyle

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