Re: [GIT PULL] Update LZO compression

[Johannes Stezenbach <js@sig21.net>]

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Hi Marcus,

On Wed, Aug 15, 2012 at 02:02:43PM +0200, Markus F.X.J. Oberhumer wrote:
> On 2012-08-14 14:39, Johannes Stezenbach wrote:
> > On Tue, Aug 14, 2012 at 01:44:02AM +0200, Markus F.X.J. Oberhumer wrote:
> >> On 2012-07-16 20:30, Markus F.X.J. Oberhumer wrote:
> >>>
> >>> As stated in the README this version is significantly faster (typically more
> >>> than 2 times faster!) than the current version, has been thoroughly tested on
> >>> x86_64/i386/powerpc platforms and is intended to get included into the
> >>> official Linux 3.6 or 3.7 release.
> >>>
> >>> I encourage all compression users to test and benchmark this new version,
> >>> and I also would ask some official LZO maintainer to convert the updated
> >>> source files into a GIT commit and possibly push it to Linus or linux-next.
> > 
> > Sorry for not reporting earlier, but I didn't have time to do real
> > benchmarks, just a quick test on ARM926EJ-S using barebox,
> > and found in the new version decompression is slower:
> > http://lists.infradead.org/pipermail/barebox/2012-July/008268.html
> 
> I can only guess, but maybe your ARM cpu does not have an efficient
> implementation of {get,put}_unaligned().

Yes, ARMv5 cannot do unaligned access.  ARMv6+ could, but
I think the Linux kernel normally traps it for debug,
all ARM seem to use generic {get,put}_unaligned() implementation
which use byte access and shift.

> Could you please try the following patch and test if you can see
> any significant speed difference?

It isn't.  I made the attached quick hack userspace code
using ARM kernel headers and barebox unlzop code.
(new == your new code, old == linux-3.5 git, test == new + your suggested change)
(sorry I had no time to clean it up)

I compressed a Linux Image with lzop (lzop <arch/arm/boot/Image >lzoimage)
and timed uncompression:

# time ./unlzopold <lzoimage >/dev/null
real    0m 0.29s
user    0m 0.19s
sys     0m 0.10s
# time ./unlzopold <lzoimage >/dev/null
real    0m 0.29s
user    0m 0.20s
sys     0m 0.09s
# time ./unlzopnew <lzoimage >/dev/null
real    0m 0.41s
user    0m 0.30s
sys     0m 0.10s
# time ./unlzopnew <lzoimage >/dev/null
real    0m 0.40s
user    0m 0.30s
sys     0m 0.10s
# time ./unlzopnew <lzoimage >/dev/null
real    0m 0.40s
user    0m 0.29s
sys     0m 0.11s
# time ./unlzoptest <lzoimage >/dev/null
real    0m 0.39s
user    0m 0.28s
sys     0m 0.11s
# time ./unlzoptest <lzoimage >/dev/null
real    0m 0.39s
user    0m 0.27s
sys     0m 0.11s
# time ./unlzoptest <lzoimage >/dev/null
real    0m 0.39s
user    0m 0.27s
sys     0m 0.11s

FWIW I also checked the sha1sum to confirm the Image uncompressed OK.


Johannes

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