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On 10/10/13 20:18, Richard Yao wrote:
> Thanks for letting us know about this. I have a few comments:
>
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> 1. We could eliminate a branch entirely by doing this:
>
> mlen = MIN(d_end - dst, mlen); while (--mlen >= 0) *dst++ = *cpy++
I don't think this eliminates the branching as MIN is usually a macro
that expands to a > b ? b : a.
> 2. This optimization could become a generic optimization pass in
> the system compiler. If anyone wants to be helpful, I would
> suggest sending this patch to the developers of both LLVM and GCC.
I would ask a LLVM developers for that. If you know any GCC
developer, it would be great to let them know as well.
> 3. Have any benchmarks been done to quantify the performance
> improvement? That should not be required to merge this, but if any
> benchmarks have been done, I would like to see them for my own
> curiosity.
Well to tell the truth I didn't benchmarked the code because looking
at the assembler, the change is quite clearly an improvement (smaller
code inside the loop and the actual working code is quite simple).
The author did some benchmarks and claims to have 6% to 10%
improvement over the previous version of code with various different
types of data, but it is still interesting if someone would do a
scientific benchmark.
> On 10/10/2013 10:39 PM, Xin Li wrote:
>> Hi,
>>
>> FYI, I think you may be interested in one of our (FreeBSD)
>> recent change to lzjb decompression.
>>
>> FreeBSD r256132:
>>
>> Improve lzjb decompress performance by reorganizing the code to
>> tighten the copy loop.
>>
>> Received: from [64.62.153.212] (helo=anubis.delphij.net) by
>> node002.open-zfs.net with esmtp (HybridCluster distributed mail
>> proxy) (envelope-from <[email protected]>); Fri, 11 Oct 2013
>> 02:39:10 -0000 Submitted by: Denis Ahrens <denis h3q com>
>>
>> Should I file a ticket for this for tracking?
>>
>> Cheers,
>>
>>
>>
>> _______________________________________________ developer
>> mailing list [email protected]
>> http://lists.open-zfs.org/mailman/listinfo/developer
>>
>
>
- --
Xin LI <[email protected]> https://www.delphij.net/
FreeBSD - The Power to Serve! Live free or die
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