[Zlib-devel] Performance patch set

Stefan Fuhrmann stefanfuhrmann at alice-dsl.de
Mon May 10 04:52:01 EDT 2010

Joakim Tjernlund wrote:
>> Hi devs,
>> as I wrote some time ago, I have been working on
>> Subversion performance issues and came across
>> some optimization potential in zlib as well.
>> Inflate is now about 50% faster and a few minor
>> optimizations for deflate were done along the way,
>> too.
>> Although the changes are mostly independent
>> from each other, it would have been difficult to
>> create truly independent patches. Therefore, it's
>> all in one package. The patch was made against
>> 1.2.5 release version.
> Hi
> I just browsed your patch and noticed you are touching inffast where
> I already have an optimization pending. I thing it would be
> useful for you too. See below.
Hi Jocke!

I had noticed your work but wasn't sure whether it
already got accepted and so on. So, I decided to
post a patch that only contains my ideas.

 From what I understood, it should be possible to
add your changes to mine. You did:

* align the target memory address
  -> I will give it a try. Since we can only align
  one side of the copy, the other may still be unaligned.
  So, you reduce the frequency of unaligned accesses
  from 50% to 25%.

* copy in larger chunks
  -> I do that as well. With (sometimes much) larger chunks.
  The new idea is that you don't have to worry about
  the 'len' value: you can copy more, i.e. if the next chunk
  would partially exceed len, you can still copy it.

* memset for dist==1
  -> I tried that but it had no measurable effect
  because it was too rare. But I may just re-add it
  since the 'dist is too short' case is relatively rare
  in my case anyway. Adding checks there won't
  hurt the overall performance.

-- Stefan^2.

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