Messages in this thread Patch in this message | | | From | David Ahern <> | Subject | [PATCH] perf: sample after exit loses thread correlation - v3 | Date | Thu, 1 Aug 2013 21:52:31 -0600 |
| |
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 - 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
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> 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 | 37 +++++++++++++++++++------------------ 1 file changed, 19 insertions(+), 18 deletions(-)
diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c index f9f9d63..0d29b1b 100644 --- a/tools/perf/util/machine.c +++ b/tools/perf/util/machine.c @@ -994,11 +994,27 @@ 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); @@ -1011,27 +1027,12 @@ 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); - if (dump_trace) perf_event__fprintf_task(event, stdout); - if (thread != NULL) - machine__remove_thread(machine, thread); - return 0; } -- 1.7.10.1
| |