linux-kernel - Re: [PATCH] crypto: x86/crc32c-intel

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Message-ID: <X9fN7mOMdn1Dxn63@sol.localdomain>
Date:   Mon, 14 Dec 2020 12:41:18 -0800
From:   Eric Biggers <ebiggers@...nel.org>
To:     Tony W Wang-oc <TonyWWang-oc@...oxin.com>
Cc:     herbert@...dor.apana.org.au, davem@...emloft.net,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, x86@...nel.org,
        hpa@...or.com, linux-crypto@...r.kernel.org,
        linux-kernel@...r.kernel.org, TimGuo-oc@...oxin.com,
        CooperYan@...oxin.com, QiyuanWang@...oxin.com,
        HerryYang@...oxin.com, CobeChen@...oxin.com, SilviaZhao@...oxin.com
Subject: Re: [PATCH] crypto: x86/crc32c-intel - Don't match some Zhaoxin CPUs

On Mon, Dec 14, 2020 at 10:28:19AM +0800, Tony W Wang-oc wrote:
> On 12/12/2020 01:43, Eric Biggers wrote:
> > On Fri, Dec 11, 2020 at 07:29:04PM +0800, Tony W Wang-oc wrote:
> >> The driver crc32c-intel match CPUs supporting X86_FEATURE_XMM4_2.
> >> On platforms with Zhaoxin CPUs supporting this X86 feature, When
> >> crc32c-intel and crc32c-generic are both registered, system will
> >> use crc32c-intel because its .cra_priority is greater than
> >> crc32c-generic. This case expect to use crc32c-generic driver for
> >> some Zhaoxin CPUs to get performance gain, So remove these Zhaoxin
> >> CPUs support from crc32c-intel.
> >>
> >> Signed-off-by: Tony W Wang-oc <TonyWWang-oc@...oxin.com>
> > 
> > Does this mean that the performance of the crc32c instruction on those CPUs is
> > actually slower than a regular C implementation?  That's very weird.
> > 
> 
> From the lmbench3 Create and Delete file test on those chips, I think yes.
> 

Did you try measuring the performance of the hashing itself, and not some
higher-level filesystem operations?

- Eric