1. 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

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

3. 7.0.1.migrate vs 7.0.1.m, apparent differences
Why were there differences?
Ran 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 migrate to 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 m and migrate are the same
4 August 2010

4. 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

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

6. 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