Messages in this thread Patch in this message | | | Date | Sun, 6 Jan 2019 14:25:09 +0100 | From | Jiri Olsa <> | Subject | Re: [PATCH] perf stat: Poll for monitored tasks being alive in fork mode |
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On Sat, Jan 05, 2019 at 11:16:40AM +0800, Jin, Yao wrote: > > > 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.
ah right, -1 is special.. however that can still happen also in the orginal patch.. how about we do something like below
jirka
--- diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c index acfd48db52dd..c322cb271180 100644 --- a/tools/perf/builtin-stat.c +++ b/tools/perf/builtin-stat.c @@ -583,6 +583,14 @@ 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)) { + int pid = child_pid; + + if (pid != -1) + kill(pid, SIGTERM); + break; + } + nanosleep(&ts, NULL); if (timeout) break;
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