linux-kernel - Re: [GIT PULL] Update LZO compression

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Date:	Wed, 15 Aug 2012 14:02:43 +0200
From:	"Markus F.X.J. Oberhumer" <markus@...rhumer.com>
To:	Johannes Stezenbach <js@...21.net>
CC:	linux-kernel@...r.kernel.org, Andi Kleen <andi@...stfloor.org>,
	chris.mason@...ionio.com, linux-btrfs@...r.kernel.org,
	Nitin Gupta <ngupta@...are.org>,
	Richard Purdie <rpurdie@...nedhand.com>,
	richard -rw- weinberger <richard.weinberger@...il.com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [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@...rhumer.com>, http://www.oberhumer.com/
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