Messages in this thread | | | Date | Sun, 15 Nov 2009 10:13:43 +0100 | From | Ingo Molnar <> | Subject | Re: perf stat output |
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* Lucas De Marchi <lucas.de.marchi@gmail.com> wrote:
> Hi all! > > Some questions about perf stat output. See example: > > > lucas@LMS-linux:~/programming/testprograms> perf stat -e > L1-dcache-loads -e L1-dcache-load-misses -- make -j > gcc test_schedchanges.c -o test_schedchanges > gcc -pthread test_taskaff1.c -o test_taskaff1 > gcc -pthread test_taskaff2.c -o test_taskaff2 > gcc -pthread test_taskaff3.c -o test_taskaff3 > > Performance counter stats for 'make -j': > > 161384667 L1-dcache-loads # 0.000 M/sec > 24853791 L1-dcache-load-misses # 0.000 M/sec > > 0.066893389 seconds time elapsed > > Why do we have both L1-dcache-loads and L1-dcache-load-misses with > 0.000 M/sec? Also, why do we have 0 M/s when running "perf stat -a -e > cache-misses -e cache-references" but values different than 0 when > running "perf stat -a" without selecting the events?
You need the 'task-clock' event to be able to see M/sec metrics. I.e.:
$ perf stat -e L1-dcache-loads -e L1-dcache-load-misses -e task-clock sleep 1
Performance counter stats for 'sleep 1':
201330 L1-dcache-loads # 566.234 M/sec 29916 L1-dcache-load-misses # 84.138 M/sec 0.355560 task-clock-msecs # 0.000 CPUs
1.000621650 seconds time elapsed
I agree with you that seeing '0.000 M/sec' is confusing and incorrect as well. One solution would be to skip the printout in that case.
You can find the latest 'perf' code in:
http://people.redhat.com/mingo/tip.git/README
( the tools/perf/ bits are backwards compatible with any perf kernel you are running right now, so no reboot is needed. )
You can find the stats printing in tools/perf/builtin-stat.c, in the abs_printout() function:
} else { total = avg_stats(&runtime_nsecs_stats);
if (total) ratio = 1000.0 * avg / total;
fprintf(stderr, " # %10.3f M/sec", ratio);
I think if runtime_nsecs_stats is zero (i.e. if no 'task-clock' events were measured), then we might be able to skip the printout via doing something like:
} else if (runtime_nsecs_stats.n != 0) {
Would you be interested in sending a (tested) patch for that? In theory only that oneliner change should suffice - but i have not tested it.
Ingo
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