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

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

[Stephane Eranian]

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;

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

[David Ahern]

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>

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

[Arnaldo Carvalho de Melo]

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

[tip:perf/core] perf tools: fix broken perf record -a mode

[tip-bot for Stephane Eranian]

Commit-ID:  6b1bee9035d430c4b4f586df6df4b3f840e89b5b
Gitweb:     http://git.kernel.org/tip/6b1bee9035d430c4b4f586df6df4b3f840e89b5b
Author:     Stephane Eranian <eranian@google.com>
AuthorDate: Tue, 21 Feb 2012 15:54:25 +0100
Committer:  Arnaldo Carvalho de Melo <acme@redhat.com>
CommitDate: Tue, 21 Feb 2012 15:05:43 -0200

perf tools: fix broken perf record -a mode

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.

Acked-by: David Ahern <dsahern@gmail.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20120221145424.GA6757@quad
Signed-off-by: Stephane Eranian <eranian@google.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 tools/perf/util/thread_map.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

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;