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Subject[PATCH 3/6] perf offcpu: Check process id for the given workload
Date
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@kernel.org>
---
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
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