Messages in this thread | | | Date | Tue, 20 Aug 2013 12:04:01 -0600 | From | David Ahern <> | Subject | Re: [PATCH] perf: sample after exit loses thread correlation - v4 |
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ping
On 8/14/13 8:49 AM, David Ahern wrote: > Occassionally events (e.g., context-switch, sched tracepoints) are losing > the conversion of sample data associated with a thread. For example: > > $ perf record -e sched:sched_switch -c 1 -a -- sleep 5 > $ perf script > <selected events shown> > ls 30482 [000] 1379727.583037: sched:sched_switch: prev_comm=ls prev_pid=30482 ... > ls 30482 [000] 1379727.586339: sched:sched_switch: prev_comm=ls prev_pid=30482 ... > :30482 30482 [000] 1379727.589462: sched:sched_switch: prev_comm=ls prev_pid=30482 ... > > The last line lost the conversion from tid to comm. If you look at the events > (perf script -D) you see why - a SAMPLE event is generated after the EXIT: > > 0 1379727589449774 0x1540b0 [0x38]: PERF_RECORD_EXIT(30482:30482):(30482:30482) > 0 1379727589462497 0x1540e8 [0x80]: PERF_RECORD_SAMPLE(IP, 1): 30482/30482: 0xffffffff816416f1 period: 1 addr: 0 > ... thread: :30482:30482 > > When perf processes the EXIT event the thread is moved to the dead_threads > list. When the SAMPLE event is processed no thread exists for the pid so a new > one is created by machine__findnew_thread. > > This patch address the problem by delaying the move to the dead_threads list > until the tid is re-used (per Adrian's suggestion). > > With this patch we get the previous example shows: > > ls 30482 [000] 1379727.583037: sched:sched_switch: prev_comm=ls prev_pid=30482 ... > ls 30482 [000] 1379727.586339: sched:sched_switch: prev_comm=ls prev_pid=30482 ... > ls 30482 [000] 1379727.589462: sched:sched_switch: prev_comm=ls prev_pid=30482 ... > > and > > 0 1379727589449774 0x1540b0 [0x38]: PERF_RECORD_EXIT(30482:30482):(30482:30482) > 0 1379727589462497 0x1540e8 [0x80]: PERF_RECORD_SAMPLE(IP, 1): 30482/30482: 0xffffffff816416f1 period: 1 addr: 0 > ... thread: ls:30482 > > v4: per Arnaldo's request add dead flag to thread struct and set when task exits > > v3: re-do from a time based check to a delayed move to dead_threads list > > v2: Rebased to latest perf/core branch. Changed time comparison to use > a macro which explicitly shows the time basis > > Signed-off-by: David Ahern <dsahern@gmail.com> > Acked-by: Adrian Hunter <adrian.hunter@intel.com> > Cc: Frederic Weisbecker <fweisbec@gmail.com> > Cc: Ingo Molnar <mingo@kernel.org> > Cc: Jiri Olsa <jolsa@redhat.com> > Cc: Mike Galbraith <efault@gmx.de> > Cc: Namhyung Kim <namhyung@kernel.org> > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Stephane Eranian <eranian@google.com> > Cc: Adrian Hunter <adrian.hunter@intel.com> > --- > tools/perf/util/machine.c | 34 ++++++++++++++++++++-------------- > tools/perf/util/thread.h | 5 +++++ > 2 files changed, 25 insertions(+), 14 deletions(-) > > diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c > index 4514e7e..574feb7 100644 > --- a/tools/perf/util/machine.c > +++ b/tools/perf/util/machine.c > @@ -1031,11 +1031,27 @@ out_problem: > return 0; > } > > +static void machine__remove_thread(struct machine *machine, struct thread *th) > +{ > + machine->last_match = NULL; > + rb_erase(&th->rb_node, &machine->threads); > + /* > + * We may have references to this thread, for instance in some hist_entry > + * instances, so just move them to a separate list. > + */ > + list_add_tail(&th->node, &machine->dead_threads); > +} > + > int machine__process_fork_event(struct machine *machine, union perf_event *event) > { > - struct thread *thread = machine__findnew_thread(machine, event->fork.tid); > + struct thread *thread = machine__find_thread(machine, event->fork.tid); > struct thread *parent = machine__findnew_thread(machine, event->fork.ptid); > > + /* if a thread currently exists for the thread id remove it */ > + if (thread != NULL) > + machine__remove_thread(machine, thread); > + > + thread = machine__findnew_thread(machine, event->fork.tid); > if (dump_trace) > perf_event__fprintf_task(event, stdout); > > @@ -1048,18 +1064,8 @@ int machine__process_fork_event(struct machine *machine, union perf_event *event > return 0; > } > > -static void machine__remove_thread(struct machine *machine, struct thread *th) > -{ > - machine->last_match = NULL; > - rb_erase(&th->rb_node, &machine->threads); > - /* > - * We may have references to this thread, for instance in some hist_entry > - * instances, so just move them to a separate list. > - */ > - list_add_tail(&th->node, &machine->dead_threads); > -} > - > -int machine__process_exit_event(struct machine *machine, union perf_event *event) > +int machine__process_exit_event(struct machine *machine __maybe_unused, > + union perf_event *event) > { > struct thread *thread = machine__find_thread(machine, event->fork.tid); > > @@ -1067,7 +1073,7 @@ int machine__process_exit_event(struct machine *machine, union perf_event *event > perf_event__fprintf_task(event, stdout); > > if (thread != NULL) > - machine__remove_thread(machine, thread); > + thread__exited(thread); > > return 0; > } > diff --git a/tools/perf/util/thread.h b/tools/perf/util/thread.h > index 13c62c9..32d0601 100644 > --- a/tools/perf/util/thread.h > +++ b/tools/perf/util/thread.h > @@ -16,6 +16,7 @@ struct thread { > pid_t ppid; > char shortname[3]; > bool comm_set; > + bool dead; /* if set thread has exited */ > char *comm; > int comm_len; > > @@ -26,6 +27,10 @@ struct machine; > > struct thread *thread__new(pid_t tid); > void thread__delete(struct thread *self); > +static inline void thread__exited(struct thread *thread) > +{ > + thread->dead = true; > +} > > int thread__set_comm(struct thread *self, const char *comm); > int thread__comm_len(struct thread *self); >
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