Improve LHEReader IO (and optimize skipping events)

[bbockelm]

This branch does two things:

1. Buffers LHEReader IO along 16MB boundaries (both compressed and uncompressed cases).
2. Skips parsing of events that will be skipped.

When testing (2), I found there was 1.8x speedup when reading compressed files and 1.9x speedup when reading uncompressed files. This suggests, when there is efficient IO, we are dominated by XML parsing times (not decompression times).

@davidlange6 @bendavid

[cmsbuild]

A new Pull Request was created by @bbockelm (Brian Bockelman) for CMSSW_7_1_X.

Improve LHEReader IO (and optimize skipping events)

It involves the following packages:

GeneratorInterface/LHEInterface

@vciulli, @cmsbuild, @covarell, @bendavid, @thuer can you please review it and eventually sign? Thanks.
@mkirsano this is something you requested to watch as well.
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@Degano you are the release manager for this.
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[bendavid]

This cout should probably be removed.

[bbockelm]

Good catch - development cout's removed.

[cmsbuild]

Pull request #10287 was updated. @vciulli, @cmsbuild, @covarell, @bendavid, @thuer can you please check and sign again.

[bendavid]

+1

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_1_X IBs once checked with relvals in the development release cycle of CMSSW or unless it breaks tests. This pull request requires discussion in the ORP meeting before it's merged. @davidlange6, @Degano, @smuzaffar

[bbockelm]

@bendavid @davidlange6 - should I do another PR for 7_6_X?

[bendavid]

Did it already
#10431

[bbockelm]

Thanks!

Is there any final summary of the performance improvements? I know the real world sometimes differs from my development VM.

I suppose just giving me a heads-up when the affected SUSY LHE gets resubmitted.