Messages in this thread | | | Subject | Re: [PATCH] perf stat: Poll for monitored tasks being alive in fork mode | From | "Jin, Yao" <> | Date | Sat, 5 Jan 2019 11:16:40 +0800 |
| |
On 1/4/2019 8:54 PM, Jiri Olsa wrote: > On Fri, Jan 04, 2019 at 10:28:17AM +0800, Jin Yao wrote: >> Following test shows the stat keeps running even if no longer >> task to monitor (mgen exits at ~5s). >> >> perf stat -e cycles -p `pgrep mgen` -I1000 -- sleep 10 >> time counts unit events >> 1.000148916 1,308,365,864 cycles >> 2.000379171 1,297,269,875 cycles >> 3.000556719 1,297,187,078 cycles >> 4.000914241 761,261,827 cycles >> 5.001306091 <not counted> cycles >> 6.001676881 <not counted> cycles >> 7.002046336 <not counted> cycles >> 8.002405651 <not counted> cycles >> 9.002766625 <not counted> cycles >> 10.001395827 <not counted> cycles >> >> We'd better finish stat immediately if there's no longer task to >> monitor. >> >> After: >> >> perf stat -e cycles -p `pgrep mgen` -I1000 -- sleep 10 >> time counts unit events >> 1.000180062 1,236,592,661 cycles >> 2.000421539 1,223,733,572 cycles >> 3.000609910 1,297,047,663 cycles >> 4.000807545 1,297,215,816 cycles >> 5.001001578 1,297,208,032 cycles >> 6.001390345 582,343,659 cycles >> sleep: Terminated >> >> Now the stat exits immediately when the monitored tasks ends. >> >> Signed-off-by: Jin Yao <yao.jin@linux.intel.com> >> --- >> tools/perf/builtin-stat.c | 7 +++++++ >> 1 file changed, 7 insertions(+) >> >> diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c >> index 63a3afc..71f3bc8 100644 >> --- a/tools/perf/builtin-stat.c >> +++ b/tools/perf/builtin-stat.c >> @@ -553,6 +553,13 @@ static int __run_perf_stat(int argc, const char **argv, int run_idx) >> >> if (interval || timeout) { >> while (!waitpid(child_pid, &status, WNOHANG)) { >> + if (!is_target_alive(&target, >> + evsel_list->threads) && >> + (child_pid != -1)) { > > do we need that child_pid check? we just returned from waitpid > so we should be ok.. we just make the race window smaller > > could we just do: > > if (!is_target_alive(&target, evsel_list->threads)) { > kill(child_pid, SIGTERM); > break; > } >
I think this code should be OK and I have tested yet. I have a question about the race condition, we really don't need a lock to protect the child_pid?
skip_signal() { /* * render child_pid harmless * won't send SIGTERM to a random * process in case of race condition * and fast PID recycling */ child_pid = -1; }
__run_perf_stat() { .... kill(child_pid, SIGTERM); }
If child_pid is set by -1 in a small window between checking of child_pid and kill(), then kill(-1, SIGTERM) may happen. All processes except the kill process itself and init would receive SIGTERM.
Is this case possible?
> also I'm not sure we should do this only under new option, > as it might break people's scripts.. thoughts? > > jirka >
In current behavior, for non fork mode, if we terminate the monitored task, the perf stat would return immediately. So I think this patch should be OK.
Thanks Jin Yao
>> + kill(child_pid, SIGTERM); >> + break; >> + } >> + >> nanosleep(&ts, NULL); >> if (timeout) >> break; >> -- >> 2.7.4 >>
| |