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

Arnaldo Carvalho de Melo
2012-02-21T17:08:04Z

Em Tue, Feb 21, 2012 at 08:31:56AM -0700, David Ahern escreveu:
> 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.

Stephane,

Feel free to submit a patch :-)

>> 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>

Yeah, this one slip thru my visual inspection :-\

Now I'll pay for this sin by adding an entry in 'perf test' to check
that :-)

- Arnaldo