linux-kernel - Re: [dm-devel] [PATCH] DM-CRYPT: Scale to multiple CPUs

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Date:	Tue, 01 Jun 2010 08:40:46 +0200
From:	Andi Kleen <ak@...ux.intel.com>
To:	Mikulas Patocka <mpatocka@...hat.com>
CC:	device-mapper development <dm-devel@...hat.com>,
	herbert@...dor.hengli.com.au, linux-kernel@...r.kernel.org,
	agk@...hat.com
Subject: Re: [dm-devel] [PATCH] DM-CRYPT: Scale to multiple CPUs

, Mikulas Patocka wrote:
> Questions:
>
> If you are optimizing it,
>
> 1) why don't you optimize it in such a way that if one CPU submits
> requests, the crypto work is spread among all the CPUs? Currently it
> spreads the work only if different CPUs submit it.

This case is only useful with very slow CPUs and is handled by pcrypt
in theory

(but I haven't tested it)

>
> 2) why not optimize software async crypto daemon (crypt/cryptd.c) instead
> of dm-crypt, so that all kernel subsystems can actually take advantage of
> those multi-CPU optimizations, not just dm-crypt?

Normally most subsystems are multi-CPU already, unless they limit
themselves artitifically like dm-crypt.

For dm-crypt would be wasteful to funnel everything through two single CPU threads just
to spread it out again.  That is why I also used per CPU IO threads too.

-Andi


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