linux-kernel - Re: comparison of the AF_ALG interface with the /dev/crypto

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Date:	Thu, 01 Sep 2011 08:26:07 +0200
From:	Nikos Mavrogiannopoulos <nmav@...tls.org>
To:	Herbert Xu <herbert@...dor.hengli.com.au>
CC:	cryptodev-linux-devel@....org, linux-crypto@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: comparison of the AF_ALG interface with the /dev/crypto

On 09/01/2011 04:15 AM, Herbert Xu wrote:
> Nikos Mavrogiannopoulos<nmav@...tls.org>  wrote:
>>
>> Given my benchmarks have no issues, it is not apparent to me why one
>> should use AF_ALG instead of cryptodev. I do not know though why AF_ALG
>> performs so poor. I'd speculate by blaming it on the usage of the socket
>> API and the number of system calls required.
> The target usage of AF_ALG is hardware offload devices that cannot
> be directly used in user-space, not software crypto on implementations
> such as AESNI/Padlock.
> Going through the kernel to use something like AESNI/Padlock or
> software crypto is insane.
> Given the intended target case, your numbers are pretty much
> meaningless as cryptodev's performance can be easily beaten
> by a pure user-space implementation.

Actually this is the reason of the ecb(cipher-null) comparison. To 
emulate the case of a hardware offload device. I tried to make that 
clear in the text, but may not be. If you see AF_ALG performs really bad 
on that case. It performs better when a software or a padlock 
implementation of AES is involved (which as you say it is a useless 
use-case).

Of course, I don't own such an offloading device and cannot test it 
directly. If you have different values from a benchmark with an actual 
hardware accelerator, I'll be happy to include them.

regards,
Nikos
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