Optimization of PixelHitMatcher

[lgray]

Factor of 3.5 speed up in ecalDrivenElectronSeeds producer.
4x speed up in compatibleSeeds() function in PixelHitMatcher class.
Mostly this comes from using hash tables, some speedup from not using GlobalPoint::phi() all the time and lazy returns.
Timing measurements are from TTBar 25ns@40PU.

No regressions expected.
In local testing of single electron gun and ttbar 25ns, no regressions observed.

@VinInn

[cmsbuild]

A new Pull Request was created by @lgray (Lindsey Gray) for CMSSW_7_1_X.

Optimization of PixelHitMatcher

It involves the following packages:

RecoEgamma/EgammaElectronAlgos

@nclopezo, @cmsbuild, @anton-a, @thspeer, @slava77, @Degano can you please review it and eventually sign? Thanks.
You can sign-off by replying to this message having '+1' in the first line of your reply.
You can reject by replying to this message having '-1' in the first line of your reply.
@nclopezo, @ktf you are the release manager for this.
You can merge this pull request by typing 'merge' in the first line of your comment.

[cmsbuild]

+1
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-3020/667/summary.html

[slava77]

checking

[slava77]

Looking at 202.0 (2012-like TTBar PU) on 200 events with igprof I see only 10% improvement from PixelHitMatcher::compatibleSeeds: going from 15 perf ticks to 13.6.
Most notable part here is that inside this function the call to PropagatorWithMaterial::propagateWithPath has doubled in weight from 4 to 8 ticks.

[VinInn]

at pileup 40 25ns is very different
this is the a recent IB for TTBAR PU40 25ns
http://innocent.web.cern.ch/innocent/perfResults/igprof-navigator/TTBAR_step3_ori_CMSSW_7_1_X_2014-03-14-0200_slc6_amd64_gcc490/103
notice rank 103
(compare with yours)

this is jetHT run2012C
http://innocent.web.cern.ch/innocent/perfResults/igprof-navigator/step2_Run2012C_Candidate_CMSSW_7_1_X_2014-03-28-0200_slc6_amd64_gcc481/365
(should be similar to yours)
here is at rank 365

very very different contributions to
PixelHitMatcher::compatibleSeeds
in the two cases

[slava77]

I see, so ::estimate vs ::propagate calls are quite different in relative weight.
Other that ::propagate, the total of all other calls inside PixelHitMatcher::compatibleSeeds goes down by x2 in my wf 202.0. I can understand that this goes up with higher occupancy.
Still, an increase in calls to ::propagate is strange.

[slava77]

+1

for #3020 6760ed8
tested in CMSSW_7_1_X_2014-03-25-1400 (my test area sign329)

no differences in outputs, as expected.
The summary/discussion for timing is above. the increase in ::propagate looks odd, could be fixed later, I suppose, if it's a real.

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_1_X IBs unless changes (tests are also fine). @nclopezo, @ktf can you please take care of it?