James N. Bellinger University of Wisconsin at Madison 4 August 2010 Code Migration James N. Bellinger University of Wisconsin at Madison 4 August 2010 4 July 2010

Executive summary 7.0.1.m differences are not real, bug in KS test While investigating, other “curiosities” appeared 4 August 2010

7.0.1.migrate vs 7.0.1.m, apparent differences Why were there differences? Ran 7.0.1.m on the same file, twice, using maxopt Processed using non-opt stnmaker and histogram generator Compared using usual histogram comparator Voila: same different histograms as comparing 7.0.1.migrate to 7.0.1.m; all in TProfile plots You don’t get the same results twice in a row using the same data? Why not? Perhaps we are using uninitialized data somewhere Started valgrind job to check this Perhaps there was a bug in the checking program Dumped the histogram contents THESE WERE IDENTICAL. It looks like 7.0.1.m and 7.0.1.migrate are the same 4 August 2010

While searching for the difference Running valgrind on maxopt ProductionExe Not guaranteed, optimizations can confuse it Run again with non-optimized and compare Job not done yet So far it complains about oracle_client and root using uninitialized data AND Complained about KalUtils::forwardFit2COT, where Prof. Herndon verified that a known defect exists 4 August 2010

Where is the problem in our code? 306 if (track->fit().layer[track->fit().innermostlay_]==0&&track->fit().innermostlay_==1) { 307 while (track->fit().layer[track->fit().innermostlay_]==0) { 308 track->fit().innermostlay_ = track->fit().innermostlay_+1; 309 } 310 } The real problem is elsewhere: the test at line 306 is a work-around to keep it from crashing 4 August 2010

What next? Maybe we can add sanity checking code where we use oracle (or this may be known to be harmless) We could get root code and fix it for our own use (this may be harmless too) Side effect of packing memory in blocks? Tracking code: we could generate some experts and find the bug (original authors are gone from HEP) Or we could say that the cloud is still no bigger than a man’s hand, the workaround works, and forge ahead anyway 4 August 2010