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AES performance
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"Bert Belder"  
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 More options Sep 19 2012, 5:50 pm
Newsgroups: mailing.openssl.dev
From: bertbel...@gmail.com ("Bert Belder")
Date: Wed, 19 Sep 2012 23:49:44 +0200
Local: Wed, Sep 19 2012 5:49 pm
Subject: AES performance
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Hey all,

Within aes-x86_64.pl, I found this code:

        mov     OPENSSL_ia32cap_P(%rip),%r10d
        cmp     \$$speed_limit,%rdx
        jb      .Lcbc_slow_prologue
        test    \$15,%rdx
        jnz     .Lcbc_slow_prologue
        bt      \$28,%r10d
        jc      .Lcbc_slow_prologue

The last two lines make sure that x86_64_AES_encrypt_compact is used on
processors that support hyperthreading. I found that on my machine (a retina
macbook with an Intel i7-3720QM processor) this makes AES encryption much
slower (by about 35%).

Can anyone enlighten me on why openssl wants to use the "slow" version on
machines that support hyperthreading?

Thanks in advance,
Bert

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Yann Droneaud  
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 More options Sep 25 2012, 12:01 pm
Newsgroups: mailing.openssl.dev
From: y...@droneaud.fr (Yann Droneaud)
Date: Tue, 25 Sep 2012 17:42:47 +0200
Local: Tues, Sep 25 2012 11:42 am
Subject: Re: AES performance
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Le mercredi 19 septembre 2012 à 23:49 +0200, Bert Belder a écrit :

Here is a probable explaination:
(from http://thread.gmane.org/gmane.comp.encryption.openssl.devel/19942
)

> From OpenSSL-0.9.8 to OpenSSL-1.0.0, when using ASM version, AES
> encryption speed goes down. It's not a regression: the ASM version
> was tweaked to handle some shared cache attack vector:
>From Andy Polyakov <ap...@openssl.org>:
> Assembler appears slower, because it's taking code path resistant to
> cache-timing attacks [on multi-core CPUs with shared cache].

http://thread.gmane.org/gmane.comp.encryption.openssl.devel/19836

Regards.

--
Yann Droneaud

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