linux-kernel - Re: [RFC PATCH crypto 4/4] AES-NI: Add support to Intel AES-NI instructions for x86

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Message-ID: <20090109091814.GA10881@gondor.apana.org.au>
Date:	Fri, 9 Jan 2009 20:18:14 +1100
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Huang Ying <ying.huang@...el.com>
Cc:	Sebastian Siewior <linux-crypto@...breakpoint.cc>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>
Subject: Re: [RFC PATCH crypto 4/4] AES-NI: Add support to Intel AES-NI
	instructions for x86_64 platform

On Fri, Jan 09, 2009 at 04:54:33PM +0800, Huang Ying wrote:
> 
> - cryptd thread is not per-CPU, so I think there will be some
> unnecessary cache inter-CPU migration. Why not use a dedicate workqueue

Well it shouldn't be hard to make cryptd per-cpu.

> or just system events workqueue?

That's actually bad because the system events queue is a shared
resource which is often subject to starvation problems.  On the
one hand we may be starved by others and we may also starve others
by doing too much crypto.

> - with cryptd(__*-aes-aesni), we need 4 internal tfms for each external
> tfm allocation request. For example, for one external cbc(aes) tfm
> allocation request, we need one cbc(aes) ablkcipher tfm, one
> cryptd(cbc-aes-aesni) tfm, and two cbc-aes-aesni tfm. Do we use too much
> memory? And we need to call aesni_set_key() twice.

Not at all, tfms are just "shell" objects and they were designed
to be used in thie way.  Calling setkey twice is an issue but it's
not a show-stopper.  We have the same problem in other places to
so this something that we can potentially optimise.

Cheers,
-- 
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Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
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