On Thu, Jun 09, 2005 at 10:13:13PM -0700, Shirley Ma wrote: > >I think adding such a calibration to get_cpu_mhz() > >so we can warn if /proc/cpuinfo data doesn't agree with > >gettimeofday() and get_cycles(). > > using below to calculate the cycles_to_unit is more accurate. > > clock_gettime(); > get_cycles(); > sleep(5); > clock_gettime(); > get_cycles();
While I agree in general with the concept, I don't agree with this algorithm for two reaons: o I don't trust get_cycles() to measure anything more than 1s. Problem is on some 32-bit arches, they may only have (or only read) a 32-bit cycle counter. This can wrap in as little as 2 or 3 seconds. This obviously isn't a problem with 64-bit counters. o Trivial but annoying - adding 5 seconds per run means a scripted batch job could take minutes longer. > cycles_to_unit = offset - cycles/ offset - time; I think we can effectively do the same thing by summing the recorded "get_cycles" values and compare that sum to before/after gettimeofday() readings. I'll submit a patch later today that effectively does that. grant _______________________________________________ openib-general mailing list [email protected] http://openib.org/mailman/listinfo/openib-general To unsubscribe, please visit http://openib.org/mailman/listinfo/openib-general
