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

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On Tue, Dec 13, 2011 at 09:27:10AM +0100, Joakim Tjernlund wrote:
> "Darrick J. Wong" <djwong@xxxxxxxxxx> 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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