[PATCH 3/6] perf offcpu: Check process id for the given workload

[Namhyung Kim]

Current task filter checks task->pid which is different for each
thread.  But we want to profile all the threads in the process.  So
let's compare process id (or thread-group id: tgid) instead.

Before:
  $ sudo perf record --off-cpu -- perf bench sched messaging -t
  $ sudo perf report --stat | grep -A1 offcpu
  offcpu-time stats:
            SAMPLE events:        2

After:
  $ sudo perf record --off-cpu -- perf bench sched messaging -t
  $ sudo perf report --stat | grep -A1 offcpu
  offcpu-time stats:
            SAMPLE events:      850

Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>
---
 tools/perf/util/bpf_off_cpu.c          | 1 +
 tools/perf/util/bpf_skel/off_cpu.bpf.c | 8 +++++++-
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/bpf_off_cpu.c b/tools/perf/util/bpf_off_cpu.c
index f289b7713598..7dbcb025da87 100644
--- a/tools/perf/util/bpf_off_cpu.c
+++ b/tools/perf/util/bpf_off_cpu.c
@@ -78,6 +78,7 @@ static void off_cpu_start(void *arg)
 		u8 val = 1;
 
 		skel->bss->has_task = 1;
+		skel->bss->uses_tgid = 1;
 		fd = bpf_map__fd(skel->maps.task_filter);
 		pid = perf_thread_map__pid(evlist->core.threads, 0);
 		bpf_map_update_elem(fd, &pid, &val, BPF_ANY);
diff --git a/tools/perf/util/bpf_skel/off_cpu.bpf.c b/tools/perf/util/bpf_skel/off_cpu.bpf.c
index cc6d7fd55118..143a8b7acf87 100644
--- a/tools/perf/util/bpf_skel/off_cpu.bpf.c
+++ b/tools/perf/util/bpf_skel/off_cpu.bpf.c
@@ -85,6 +85,7 @@ int enabled = 0;
 int has_cpu = 0;
 int has_task = 0;
 int has_cgroup = 0;
+int uses_tgid = 0;
 
 const volatile bool has_prev_state = false;
 const volatile bool needs_cgroup = false;
@@ -144,7 +145,12 @@ static inline int can_record(struct task_struct *t, int state)
 
 	if (has_task) {
 		__u8 *ok;
-		__u32 pid = t->pid;
+		__u32 pid;
+
+		if (uses_tgid)
+			pid = t->tgid;
+		else
+			pid = t->pid;
 
 		ok = bpf_map_lookup_elem(&task_filter, &pid);
 		if (!ok)
-- 
2.37.0.rc0.161.g10f37bed90-goog