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

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Date:	Tue, 21 Feb 2012 15:54:25 +0100
From:	Stephane Eranian <eranian@...gle.com>
To:	linux-kernel@...r.kernel.org
Cc:	dsahern@...il.com, acme@...hat.com, peterz@...radead.org,
	mingo@...e.hu, eric.dumazet@...il.com
Subject: [PATCH] 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.

Signed-off-by: Stephane Eranian <eranian@...gle.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;
--
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