Re: Per thread sampling

[Jiri Olsa <jolsa@redhat.com>]

On Wed, Feb 19, 2014 at 04:00:45PM +0100, Manuel Selva wrote:
> Hi all,
> 
> I just tried in a 2-threaded application to call twice (one call for
> each thread) perf_event_open syscall with parameters configured to do
> sampling on MEM INST RETIRED.LATENCY ABOVE THRESHOLD event. Both call
> succeed.
> 
> "mmaping" the file descriptor return by the first call succeed but
> "mmaping" the second file descriptor results in a "Operation not
> permitted" error (errno = 1).

seems like you might have crossed the perf mem user limit?

[jolsa@krava ~]$ sysctl kernel.perf_event_mlock_kb 
kernel.perf_event_mlock_kb = 516

you can either split the memory amount between those
threads or you can increase that limit.. or run your
app under root ;-)

jirka

>mit 
> A work around could be to sample all threads (with pid = -1) including
> pid and tid in samples and filter samples at processing time. Before
> switching to this solution I wanted to ask if this a known limitation
> of the syscall, an error from my side, or a bug  (the man page doesn't
> answer to this question) ?
> 
> Thanks,
> 
> Manu
> --
> To unsubscribe from this list: send the line "unsubscribe linux-perf-users" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html