Tracking: Switch off cluster shape in step6 seeding

[thspeer]

By removing the cluster shape filter in the TobTec step seeding, the efficiency for displaced tracks is increased from ~23 to ~26 %. This recovers the lost efficiency when the CCC was introduced.

[cmsbuild]

A new Pull Request was created by @thspeer for CMSSW_7_1_X.

Tracking: Switch off cluster shape in step6 seeding

It involves the following packages:

RecoPixelVertexing/PixelLowPtUtilities
RecoTracker/IterativeTracking

@nclopezo, @cmsbuild, @anton-a, @thspeer, @slava77, @Degano can you please review it and eventually sign? Thanks.
@ghellwig, @GiacomoSguazzoni, @rovere, @gpetruc, @cerati, @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.
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@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-3818/1454/summary.html

[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-3818/1454/summary.html

[slava77]

tobTecStepTrackCandidates time essentially doubles in wf 202.0 (also doubles in 25202, the PU20)
Is this expected/needed?
This is +2% in CPU in these tests.

I can guess that PU40 can go up even more.
Thomas, do you have tests for this?

Should it go to pre8 or should we better iterate on this later in 72X?

[cerati]

Indeed this is bug fix, as when the strip triplet seeding for tobTec was developed the clusterShapeFilter was intentionally left out not to lose efficiency. It went in with the CCC, but it was not intentional.
In my opinion, with the new seeding and CCC, we have reduced timing enough that we should keep efficiency as high as possible at this stage (the 2x mentioned by slava refers to a versions that is much faster than in 62X).
Maybe Thomas has the proper numbers handy?

[slava77]

It would be good to see comparisons of timing, at least as a reference.
My memory is that the last improvements in CCC (thickness-dependent cuts) had about the same effect as this PR on timing, only with a negative side. So, at least these two cancel out.

[thspeer]

In my tests, the tracking time goes from 11.6 sec/event to 12.8 sec/event. This can be compared to the 16.0 I saw in 710pre4, before the new CCC was added. So we still have a clear improvement in the timing.

[slava77]

are these the same inputs?

[thspeer]

yes, exactly the same events

[slava77]

+1

for #3818 a4acb64

tested in CMSSW_7_1_X_2014-05-13-1400 (test area sign375)
some increase in efficiency vs vtx pos without much increase in fake rate

(dijet QCD below)

changes as expected, although some finer tuning of selections may have helped (the number of seeds in iter 6 almost doubles)

[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?