Re: Fusion-ifying proto parse trees

Eric Niebler wrote:
> Joel de Guzman wrote:
> > Ok, let's put your hypothesis to test. Can we try your
> > Zero-copy expression template construction idea with the
> > current tests that you have? (i.e. seq<> holding its left
> > and right children by reference).
>
>
> The results are in. The following ET schemes were tested:
>
> 1) The Spirit2 approach: eager flattening in the ET
> 2) Non-segmented proto: Zero-copy ET construction, non-segmented ET 
> traversal.
> 3) Segmented proto: Zero-copy ET construction, segmented ET traversal.
>
> Time taken to construct the ET and traverse it was measured. The winner 
> by a wide margin is (3) segmented proto. For larger ET trees, segmented 
> proto is over 8x faster than the Spirit2 approach. (Note that even 
> non-segmented proto is marginally faster than the Spirit2 approach.)
>
> I have also reformulated the segmentation interface according to the 
> simpler scheme Joel and I discussed. It's *much* easier to work with.
>
> For kicks, I also ran the test with proto modified to hold copies of its 
> child nodes instead of references, on the chance that the cost of the 
> indirections might outweigh the cost of the copies. It doesn't. Holding 
> children by value is 2x slower than holding them by reference. (The 
> indirections do have a cost, however, so if you plan to traverse the 
> proto tree multiple times, it might make sense to deep-copy it first. 
> Proto should provide a deep-copy utility.)
>
> Attached is the test and the timing results. Be sure to sync to 
> $boost_root/boost/xpressive, as I had to make changes to proto to 
> support zero-copy ET construction.

Great! It would be nice if the 1) time taken to construct the ET
and 2) the time to traverse it, are reported separately. For spirit,
while 1 is important, 2 is more important by a wide margin. It's
a balance, I can tolerate a few clock cycles for 1 if that would
improve 2. So, it's very important to see both timings.

It would also be nice to see the App footprint, but I guess it's
too early to do that now.

Regards,
--
Joel de Guzman
http://www.boost-consulting.com
http://spirit.sf.net



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