linux-kernel - Re: [PATCH -mm crypto] AES: x86_64 asm implementation optimization

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Date:	Wed, 07 May 2008 13:26:13 +0800
From:	"Huang, Ying" <ying.huang@...el.com>
To:	Sebastian Siewior <linux-crypto@...breakpoint.cc>
Cc:	Herbert Xu <herbert@...dor.apana.org.au>,
	"Adam J. Richter" <adam@...drasil.com>, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
	mingo@...e.hu, tglx@...utronix.de
Subject: Re: [PATCH -mm crypto] AES: x86_64 asm implementation optimization

Hi, Sebastian,

On Wed, 2008-04-30 at 00:12 +0200, Sebastian Siewior wrote:
> * Huang, Ying | 2008-04-25 11:11:17 [+0800]:
> 
> >Hi, Sebastian,
> Hi Huang,
> 
> sorry for the delay.
> 
> >I changed the patches to group the read or write together instead of
> >interleaving. Can you help me to test these new patches? The new patches
> >is attached with the mail.
> The new results are attached.

It seems that the performance degradation between step4 to step5 is
decreased. But the overall performance degradation between step0 to
step7 is still about 5%.

I also test the patches on Pentium 4 CPUs, and the performance decreased
too. So I think this optimization is CPU micro-architecture dependent.

While the dependency between instructions are reduced, more registers
(at most 3) are saved/restored before/after encryption/decryption. If
the CPU has no extra execution unit for newly independent instructions
but more registers are saved/restored, the performance will decrease.

We maybe should select different implementation based on
micro-architecture.

Best Regards,
Huang Ying

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