linux-kernel - RE: [PATCH 0/6] Faster AES-XTS on modern x86

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Date: Wed, 3 Apr 2024 08:12:09 +0000
From: David Laight <David.Laight@...LAB.COM>
To: 'Eric Biggers' <ebiggers@...nel.org>, Ard Biesheuvel <ardb@...nel.org>
CC: "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, Andy Lutomirski <luto@...nel.org>, "Chang S .
 Bae" <chang.seok.bae@...el.com>
Subject: RE: [PATCH 0/6] Faster AES-XTS on modern x86_64 CPUs

From: Eric Biggers
> Sent: 26 March 2024 16:48
...
> Consider Intel Ice Lake for example, these are the AES-256-XTS encryption speeds
> on 4096-byte messages in MB/s I'm seeing:
> 
>     xts-aes-aesni                  5136
>     xts-aes-aesni-avx              5366
>     xts-aes-vaes-avx2              9337
>     xts-aes-vaes-avx10_256         9876
>     xts-aes-vaes-avx10_512         10215
> 
> So yes, on that CPU the biggest boost comes just from VAES, staying on AVX2.
> But taking advantage of AVX512 does help a bit more, first from the parts other
> than 512-bit registers, then a bit more from 512-bit registers.

How much does the kernel_fpu_begin() cost on real workloads?
(ie when the registers are live and it forces an extra save/restore)

I've not looked at the code but I often see what looks like
excessive inlining in crypto code.
This will speed up benchmarks but can have a negative effect
on real code both because of the time taken to load the
code and the effect of displacing other code.

It might be that this code is a simple loop....

	David

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