[RFC] Make HLT addOnTest GEN step to use 1 concurrent LuminosityBlock

[makortel]

PR description:

Tests of #35326 (comment) pointed out that the GEN(+others) step of the HLT addOnTests use Pythia8GeneratorFilter while using multiple threads and therefore also 2 concurrent lumis by default. The generator fragment uses Tauola, so Pythia8ConcurrentHadronizerFilter can not be used. This PR suggests to explicitly use 1 concurrent lumi in the GEN step.

If Tauola is not strictly needed, an alternative would be to change the GEN fragment to TTbar_8TeV_TuneCUETP8M1_cfi / TTbar_13TeV_TuneCUETP8M1_cfi that use Pythia8ConcurrentHadronizerFilter.

PR validation:

In a private test with #35326 the addOnTests run to completion.

[cmsbuild]

+code-checks

Logs: https://cmssdt.cern.ch/SDT/code-checks/cms-sw-PR-35350/25415

• This PR adds an extra 12KB to repository

[cmsbuild]

A new Pull Request was created by @makortel (Matti Kortelainen) for master.

It involves the following packages:

• Configuration/HLT (hlt)

@Martin-Grunewald, @missirol, @cmsbuild can you please review it and eventually sign? Thanks.
@Martin-Grunewald, @missirol, @fabiocos 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

[missirol]

If Tauola is not strictly needed, an alternative would be to change the GEN fragment to TTbar_8TeV_TuneCUETP8M1_cfi / TTbar_13TeV_TuneCUETP8M1_cfi that use Pythia8ConcurrentHadronizerFilter.

I would think that Tauola is not really necessary in this case, so we could just change the fragment. Let's see what Martin suggests.

[Martin-Grunewald]

Indeed, TTbar_13TeV_TuneCUETP8M1_cfi should be just fine.

[makortel]

Thanks, I'll prepare another PR that uses the non-Tauola TTbar GEN fragments.

[makortel]

Done in #35358