linux-ext4 - Re: [PATCH 14/14] crc32: Select an algorithm via kconfig

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Date:	Tue, 13 Dec 2011 10:36:44 -0800
From:	"Darrick J. Wong" <djwong@...ibm.com>
To:	Joakim Tjernlund <joakim.tjernlund@...nsmode.se>
Cc:	"'Andreas Dilger'" <adilger.kernel@...ger.ca>,
	"'Andrew Morton'" <akpm@...ux-foundation.org>,
	"'Mingming Cao'" <cmm@...ibm.com>,
	"'Herbert Xu'" <herbert@...dor.apana.org.au>,
	"'linux-crypto'" <linux-crypto@...r.kernel.org>,
	linux-ext4@...r.kernel.org,
	"'linux-fsdevel'" <linux-fsdevel@...r.kernel.org>,
	"'linux-kernel'" <linux-kernel@...r.kernel.org>,
	Bob Pearson <rpearson@...temfabricworks.com>,
	"'Theodore Tso'" <tytso@....edu>
Subject: Re: [PATCH 14/14] crc32: Select an algorithm via kconfig

On Tue, Dec 13, 2011 at 09:27:10AM +0100, Joakim Tjernlund wrote:
> "Darrick J. Wong" <djwong@...ibm.com> wrote on 2011/12/13 07:32:28:
> >
> > On Mon, Dec 12, 2011 at 05:10:45PM -0600, Bob Pearson wrote:
> > > That choice was for Joakim who measured better performance on his 32 bit PPC
> > > platform with "by 4".
> >
> > Ok.  On my 1.33GHz PowerBook I get ~255MB/s with slice by 4 and ~270MB/s with
> > slice by 8.  I think it's a PPC 7447, and definitely 32-bit.  In any case, it
> > reports having 32K of L1D cache.
> 
> I tested Bobs early version on my mpc8321(266MHz, embedded CPU) and it was just
> half the speed compared with current crc32.

I wonder, given the patch "crc32: Speed up memory table access on powerpc"
would you mind retesting to see if slice by 8 still trails slice by 4 on your
powerpc?  I see that your mpc8321 has 16K of L1D cache and a 32-bit memory bus
whereas my 7447 has a 64-bit memory bus.  I wonder if memory bus size could be
a defining characteristic...?

I tried it out the crc32c code on a s390x today; apparently by-8 trails by-4
there too.  It's unfortunately difficult to figure out the hardware details of
whatever's going on underneath that VM.

--D
> 
>  Jocke
> 
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