Re: [PATCH 01/17] perf report: Ask ordered events for --tasks option

Arnaldo Carvalho de Melo
2018-02-06T18:48:30Z

Em Tue, Feb 06, 2018 at 07:17:57PM +0100, Jiri Olsa escreveu:
> If we have the time in, keep the events in time order.

Try to be more verbose, what actual effect this will have in this particular
case?

So, I had to try it to see the effects and explain them:

--- /tmp/before 2018-02-06 15:40:29.536411625 -0300
+++ /tmp/after 2018-02-06 15:40:51.963403599 -0300
@@ -5,34 +5,34 @@
2540 2540 1818 | gnome-terminal-
3489 3489 2540 | bash
32433 32433 3489 | perf
- 32434 32434 32433 | perf
+ 32434 32434 32433 | make
32441 32441 32434 | make
32514 32514 32441 | make
511 511 32514 | sh
- 512 512 511 | sh
+ 512 512 511 | install

We don't have perf calling perf calling make, etc, the second perf actually is
'make', i.e. there was reordering of PERF_RECORD_COMM/PERF_RECORD_FORK:

Look for FORK and COMM meta events, for those tids:

[root@jouet acme]# perf report -D | egrep 'PERF_RECORD_(FORK|COMM)' | egrep '3243[34]'
0 14774650990679 0x1a3cd8 [0x38]: PERF_RECORD_FORK(32433:32433):(3489:3489)
1 14774652080381 0x1d6568 [0x30]: PERF_RECORD_COMM exec: perf:32433/32433
1 14774742473340 0x1dbb48 [0x38]: PERF_RECORD_FORK(32434:32434):(32433:32433)
0 14774752005779 0x1a4af8 [0x30]: PERF_RECORD_COMM exec: make:32434/32434
0 14774753997960 0x1a5578 [0x38]: PERF_RECORD_FORK(32435:32435):(32434:32434)
0 14774756070782 0x1a5618 [0x38]: PERF_RECORD_FORK(32438:32438):(32434:32434)
0 14774757772939 0x1a5680 [0x38]: PERF_RECORD_FORK(32440:32440):(32434:32434)
0 14774758230600 0x1a56e8 [0x38]: PERF_RECORD_FORK(32441:32441):(32434:32434)
[root@jouet acme]#

So they are on different CPUs, thus ring buffers, and when we don't use
ordered_events, we end up mixing that up, right?

- Arnaldo

> Link: http://lkml.kernel.org/n/tip-3wcrngoibk5l96nqyhp0nbkm@git.kernel.org
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> ---
> tools/perf/builtin-report.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/tools/perf/builtin-report.c b/tools/perf/builtin-report.c
> index 4ad5dc649716..8ef71669e7a0 100644
> --- a/tools/perf/builtin-report.c
> +++ b/tools/perf/builtin-report.c
> @@ -614,6 +614,7 @@ static int stats_print(struct report *rep)
> static void tasks_setup(struct report *rep)
> {
> memset(&rep->tool, 0, sizeof(rep->tool));
> + rep->tool.ordered_events = true;
> if (rep->mmaps_mode) {
> rep->tool.mmap = perf_event__process_mmap;
> rep->tool.mmap2 = perf_event__process_mmap2;
> --
> 2.13.6