Re: [PATCH] perf tools: fix broken perf record -a mode

David Ahern
2012-02-21T15:32:04Z

On 2/21/12 7:54 AM, Stephane Eranian wrote:
>
> The following commit:
> b52956c perf tools: Allow multiple threads or processes in record, stat, top
>
> introduced a bug in the thread_map code which caused
> perf record -a to not setup system-wide monitoring properly.
>
> $ taskset -c 1 noploop 1000&
> $ perf record -a -C 1 sleep 10
> $ perf report -D | tail -20
> cycles stats:
> TOTAL events: 4413
> MMAP events: 4025
> COMM events: 340
> SAMPLE events: 48
>
> Here I was expecting about 10,000 samples and not 48.
>
> In system-wide mode, the PID passed to perf_event_open()
> must be -1 and it was 0. That caused the kernel to setup
> a per-process event on PID:0. Consequently, the number
> of samples captured does not correspond to the requested
> measurement.
>
> The following one-liner fixes the problem for me with or
> without -C.
>
> I would also suggest to change the malloc() to something
> that matches the struct definition. thread_map->map[] is
> declared as int map[] and not pid_t map[]. If map[] can
> only contain pids, then change the struct definition.
>
> Signed-off-by: Stephane Eranian<eranian@google.com>
> ---
>
> diff --git a/tools/perf/util/thread_map.c b/tools/perf/util/thread_map.c
> index e15983c..84d9bd78 100644
> --- a/tools/perf/util/thread_map.c
> +++ b/tools/perf/util/thread_map.c
> @@ -229,7 +229,7 @@ static struct thread_map *thread_map__new_by_tid_str(const char *tid_str)
> if (!tid_str) {
> threads = malloc(sizeof(*threads) + sizeof(pid_t));
> if (threads != NULL) {
> - threads->map[1] = -1;
> + threads->map[0] = -1;
> threads->nr = 1;
> }
> return threads;

Damn. Hope you did not spend much time chasing it down.

Acked-by: David Ahern <dsahern@gmail.com>