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SubjectRe: [GIT PULL] Update LZO compression
Hi Johannes,

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().

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

Thanks,
Markus


diff --git a/lib/lzo/lzodefs.h b/lib/lzo/lzodefs.h
index ddc8db5..efc5714 100644
--- a/lib/lzo/lzodefs.h
+++ b/lib/lzo/lzodefs.h
@@ -12,8 +12,15 @@
*/


+#if defined(__arm__)
+#define COPY4(dst, src) \
+ (dst)[0] = (src)[0]; (dst)[1] = (src)[1]; \
+ (dst)[2] = (src)[2]; (dst)[3] = (src)[3]
+#endif
+#ifndef COPY4
#define COPY4(dst, src) \
put_unaligned(get_unaligned((const u32 *)(src)), (u32 *)(dst))
+#endif
#if defined(__x86_64__)
#define COPY8(dst, src) \
put_unaligned(get_unaligned((const u64 *)(src)), (u64 *)(dst))

>
> BTW, do you have userspace code matching the old and new
> lzo versions? It would be easier to benchmark.
>
> Unfortunately I cannot claim high confidence in my benchmark results
> due to missing time to do it properly, it would be useful if
> someone else could do some benchmarks on ARM before merging this.
>
>
> Johannes

--
Markus Oberhumer, <markus@oberhumer.com>, http://www.oberhumer.com/


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