Hi Joern and list(s), On Wed, Oct 14, 2009 at 12:05 PM, Joern Rennecke <joern.rennecke@xxxxxxxxxxxx> wrote: > He also said that it was a different machine, Core 2 Q6600 vs > some kind of Xeon Core 2 system with a total of eight cores. > As different memory subsystems are likely to affect the code, it > is not an established regression till he can reproduce a performance > drop going from an older to a current compiler on the same or > sufficiently similar machines, under comparable load conditions - > which generally means that the machine must be idle apart from the > benchmark. > I decided to bite the bullet and went back to GCC 4.3.4 on the same very machine where I'm experiencing the issue. With these flags: -O2 -march=core2 -fomit-frame-pointer the performance is the same as on 4.4.1 *with* -funroll-loops (actually, around 5% better, but probably it is not statistically significant). So, with 4.3.4, I get the expected *good* performance. Just to give an order of magnitude, the "good" performance measure is ~5.1-5.2 seconds, while the "bad" performance is ~11-12 seconds for this test. I ran the tests both on an idle setup (no X, just couple of services in the background) and with a "busy" machine (Firefox, audio playing in the background,...) but I could hardly notice any difference in all cases. I can try to investigate further if anyone is interested. Thanks again to everybody, Francesco PS: hope I'm not infringing the netiquette by cross-posting to two mailing lists.
