optimize memory usage in meantimer

[ptraczyk]

addressing the issue reported in https://hypernews.cern.ch/HyperNews/CMS/get/recoDevelopment/1314.html
optimize memory usage in DT local reco (algorithm output unchanged)

[cmsbuild]

A new Pull Request was created by @ptraczyk (Piotr Traczyk) for CMSSW_7_4_X.

optimize memory usage in meantimer

It involves the following packages:

RecoLocalMuon/DTSegment

@cmsbuild, @cvuosalo, @nclopezo, @slava77 can you please review it and eventually sign? Thanks.
@bellan this is something you requested to watch as well.
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[slava77]

@cmsbuild please test

Piotr, thanks for wrapping up with this.

[cmsbuild]

The tests are being triggered in jenkins.

[cmsbuild]

+1
Tested at: 061e640
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-7522/2325/summary.html

[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-7522/2325/summary.html

[cvuosalo]

Started extended test for muon workflow.

[cvuosalo]

+1

For #7522 061e640

Small code change to reduce unnecessary copying of data values and thereby reduce CPU time.

Code changes are satisfactory.

Jenkins tests show no problems or significant differences.

Workflow 20.0 (muons) was run as an extended test (2000 events) to check timing differences. The new code shows significant improvement:

delta/mean	delta/orJob	original	new	module name
-0.500873	-0.69%	16.47 ms/ev	9.87 ms/ev	dt4DSegments
-0.498409	-0.59%	14.13 ms/ev	8.49 ms/ev	dt4DCosmicSegments

Profiling also shows about a 1/3 reduction in time used by the DTMeantimer (going from a reported 2.3% of total time to 1.5%).

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_4_X IBs unless changes (tests are also fine). This pull request requires discussion in the ORP meeting before it's merged. @davidlange6, @Degano, @ktf, @smuzaffar

[davidlange6]

+1