[12_0_X] Backport the fix on the workflow 537 and the mergeLHE.py script

[colizz]

PR description:

Backport of

1. 2e7e1c0 in Enable concurrent GEN in Configuration/Generator/python #34710
2. Fix the mergeLHE.py script #34804

The first helps to fix the workflow 537 in the 4-thread mode. The issue is identified in #34531. The error is caused by a physics issue in the generator meaning that generating merely 2 events may probabilistically cause zero x-section.

The second is a relevant fix to make the mergeLHE.py script more generalized (the script is called in workflow 537), as also discussed in #34531.

PR validation:

Workflow 537 works in the 4-thread mode.

[cmsbuild]

A new Pull Request was created by @colizz (Congqiao Li) for CMSSW_12_0_X.

It involves the following packages:

• Configuration/PyReleaseValidation (pdmv, upgrade)
• GeneratorInterface/LHEInterface (generators)

@SiewYan, @mkirsano, @jordan-martins, @chayanit, @bbilin, @wajidalikhan, @Saptaparna, @cmsbuild, @AdrianoDee, @srimanob, @agrohsje, @kpedro88, @kskovpen, @alberto-sanchez, @GurpreetSinghChahal can you please review it and eventually sign? Thanks.
@mkirsano, @makortel, @Martin-Grunewald, @alberto-sanchez, @fabiocos, @slomeo this is something you requested to watch as well.
@perrotta, @dpiparo, @qliphy you are the release manager for this.

cms-bot commands are listed here

• Backported from Fix the mergeLHE.py script #34804

[perrotta]

backport of #34804
(partial) backport of #34710

[perrotta]

type bug fix

[agrohsje]

test parameters:
workflow_threading = 537.0
enable_test = threading

[agrohsje]

please test

[cmsbuild]

+1

Summary: https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-ac9eca/17832/summary.html
COMMIT: b001a8c
CMSSW: CMSSW_12_0_X_2021-08-17-1100/slc7_amd64_gcc900
Additional Tests: THREADING
User test area: For local testing, you can use /cvmfs/cms-ci.cern.ch/week0/cms-sw/cmssw/34861/17832/install.sh to create a dev area with all the needed externals and cmssw changes.

Comparison Summary

Summary:

• No significant changes to the logs found
• Reco comparison results: 3 differences found in the comparisons
• DQMHistoTests: Total files compared: 39
• DQMHistoTests: Total histograms compared: 2998564
• DQMHistoTests: Total failures: 6
• DQMHistoTests: Total nulls: 1
• DQMHistoTests: Total successes: 2998535
• DQMHistoTests: Total skipped: 22
• DQMHistoTests: Total Missing objects: 0
• DQMHistoSizes: Histogram memory added: 0.004 KiB( 38 files compared)
• DQMHistoSizes: changed ( 312.0 ): 0.004 KiB MessageLogger/Warnings
• Checked 165 log files, 37 edm output root files, 39 DQM output files
• TriggerResults: no differences found

[agrohsje]

+generators

[qliphy]

kindly ping @cms-sw/pdmv-l2 @cms-sw/upgrade-l2

[kskovpen]

+1

[qliphy]

ping @cms-sw/upgrade-l2

[srimanob]

+Upgrade

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_12_0_X IBs (tests are also fine) and once validation in the development release cycle CMSSW_12_1_X is complete. This pull request will now be reviewed by the release team before it's merged. @perrotta, @dpiparo, @qliphy (and backports should be raised in the release meeting by the corresponding L2)

[qliphy]

+1