On Mon, Mar 22, 2010 at 8:28 PM, Vince Weaver <vweav...@eecs.utk.edu> wrote: > On Mon, 22 Mar 2010, Marc Brünink wrote: >> >> short version: Is it in theory possible to get 100% accurate result for >> BR_INST_RETIRED:ANY? > > which CPU type are you running this on? > >> So: Is it possible to get a 100% accurate performance counter result (in >> theory) (for BR_INST_RETIRED:ANY)? Which are the factors distorting the >> results? Is it possible to get rid of them completely? > > I think it's interrupts again, as with the retired_instruction case. > > I ran some tests on a core2 machine using perf on a 2.6.32 core2 machine. > The test was my "ten_billion" micro-benchmark I was talking about on > Friday. > > Performance counter stats for './ten_billion': > > 10000000514 instructions # 0.000 IPC > 4999990511 branches > 1 page-faults > > 1.675311657 seconds time elapsed > > > The expected number of branches for this code is 4,999,989,996. So > the overcount is 513, which is almost exactly the same as the extra count > on retired instructions, which makes it look like the retired branch count > is also being incremented once each time an interrupt happens. > I think that's a plausible explanation. It would be interesting to verify whether the same behavior also exists on AMD processors.
> Vince > vweav...@eecs.utk.edu > ------------------------------------------------------------------------------ > Download Intel® Parallel Studio Eval > Try the new software tools for yourself. Speed compiling, find bugs > proactively, and fine-tune applications for parallel performance. > See why Intel Parallel Studio got high marks during beta. > http://p.sf.net/sfu/intel-sw-dev > _______________________________________________ > perfmon2-devel mailing list > perfmon2-devel@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/perfmon2-devel > > ------------------------------------------------------------------------------ Download Intel® Parallel Studio Eval Try the new software tools for yourself. Speed compiling, find bugs proactively, and fine-tune applications for parallel performance. See why Intel Parallel Studio got high marks during beta. http://p.sf.net/sfu/intel-sw-dev _______________________________________________ perfmon2-devel mailing list perfmon2-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/perfmon2-devel
