The CMS Monte Carlo Simulation Program: CMSIM
Picked CMSIM v111 to install on the SPP Exemplar (v112 was not yet solid)
The HP/UX binaries built at CERN ran on the SPP, but crashed with floating point errors after half a dozen events
So we recompiled all the CMSIM libraries on SPP using fort77 with -O3 (level 3 optimization)
We linked with CERNLIB HP/UX libraries built at CERN
The resulting executable ran for several tens of events before crashing with floating point errors
- We traced the problem to a bug in the CMSIM VCAL code
After correcting the bug, we measured times averaging around 3.5 minutes per fully simulated event (cf. 5.5 Minutes on a 266 MHz Pentium II for the same event set)
With 64 simultaneous CMSIM jobs running in the Exemplar, we observed a degradation to 7.5 minutes per event. This was partially due to contention on an input FZ file which was common to all 64 jobs.
Finally, we rebuilt CERNLIB with -O3 optimisation (except JETSET, GEANT321 and UCOPY2(!))
Then we made the “optimised” CMSIM, which returned 2 Minutes / event.