reduce creation of string objects and use char* instead of string

[ngrenz]

PR of a work intended to optimize gradually the perfrormance of tracker validation code.
Outputs are supposed to be unchanged.
Any comments and suggestions are welcome -more optimizations will follow in the near future

[cmsbuild]

A new Pull Request was created by @ngrenz for CMSSW_7_5_X.

reduce creation of string objects and use char* instead of string

It involves the following packages:

SimTracker/TrackerHitAssociation

@cmsbuild, @civanch, @mdhildreth can you please review it and eventually sign? Thanks.
@makortel, @GiacomoSguazzoni, @rovere, @VinInn, @appeltel, @wmtford, @cerati, @threus, @dgulhan, @venturia this is something you requested to watch as well.
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.
If you are a L2 or a release manager you can ask for tests by saying 'please test' in the first line of a comment.
@Degano you are the release manager for this.
You can merge this pull request by typing 'merge' in the first line of your comment.

[ngrenz]

@boudoul FYI

[Dr15Jones]

It would be even better to make this a const char * const. Then neither the character array nor the pointer would be allowed to change.

[makortel]

@ngrenz Have you profiled the code?

[ngrenz]

@makortel I have profiled the same change in CMSSW_7_4_0 with Igprof but not in the version 7_5_X.
The result was that funktion makeMaps was 1.5 times faster with this change.

[civanch]

@ngrenz , I would agree with Matti, that this string comparison may be done before the loop lines 108-122.

[makortel]

@ngrenz Very good, looking forward to your further optimizations.

[boudoul]

thanks all for your comments
@ngrenz : could you please update your branch with the suggestion from @makortel and @Dr15Jones ?
Thanks

[cmsbuild]

Pull request #9678 was updated. @cmsbuild, @civanch, @mdhildreth can you please check and sign again.

[ngrenz]

I had some problems with Igprof test of CMSSW_7_5_X and my simulation configuration, that is why I reconstruct the changes in 7_4_0 and profiled them with Igprof.
It is only a small simulation: 10 Events, AVE_75_BX_25ns

The results
original code:
http://test-ngrenz-igprof-result-presentation.web.cern.ch/test-ngrenz-igprof-result-presentation/cgi-bin/igprof-navigator/step3_2015-06-22_original/177

change string to char*:
http://test-ngrenz-igprof-result-presentation.web.cern.ch/test-ngrenz-igprof-result-presentation/cgi-bin/igprof-navigator/step3_2015-06-22_string/571

and change string comparison position:
http://test-ngrenz-igprof-result-presentation.web.cern.ch/test-ngrenz-igprof-result-presentation/cgi-bin/igprof-navigator/step3_2015-06-22_find/1234

and change last if position (and small variable changes):
http://test-ngrenz-igprof-result-presentation.web.cern.ch/test-ngrenz-igprof-result-presentation/cgi-bin/igprof-navigator/step3_2015-06-22_if/1145

The last result maybe slower because:

• I have made a mistake
• my reconstruction in 7_4_0 is not good
• fluctuations of the program (the number of events was low)

[cmsbuild]

Pull request #9678 was updated. @cmsbuild, @civanch, @mdhildreth can you please check and sign again.

[mdhildreth]

+1

[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-9678/5703/summary.html

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_5_X IBs once checked with relvals in the development release cycle of CMSSW (tests are also fine). This pull request requires discussion in the ORP meeting before it's merged. @davidlange6, @Degano, @smuzaffar

[davidlange6]

+1