Commit d2347763 authored by Namhyung Kim's avatar Namhyung Kim Committed by Arnaldo Carvalho de Melo
Browse files

perf offcpu: Track child processes 



When -p option used or a workload is given, it needs to handle child
processes.  The perf_event can inherit those task events
automatically.  We can add a new BPF program in task_newtask
tracepoint to track child processes.

Before:
  $ sudo perf record --off-cpu -- perf bench sched messaging
  $ sudo perf report --stat | grep -A1 offcpu
  offcpu-time stats:
            SAMPLE events:        1

After:
  $ sudo perf record -a --off-cpu -- perf bench sched messaging
  $ sudo perf report --stat | grep -A1 offcpu
  offcpu-time stats:
            SAMPLE events:      856

Signed-off-by: default avatarNamhyung Kim <namhyung@kernel.org>
Cc: Blake Jones <blakejones@google.com>
Cc: Hao Luo <haoluo@google.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Milian Wolff <milian.wolff@kdab.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Song Liu <songliubraving@fb.com>
Cc: bpf@vger.kernel.org
Link: https://lore.kernel.org/r/20220811185456.194721-4-namhyung@kernel.org


Signed-off-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
parent d6f415ca

tools/perf/util/bpf_off_cpu.c

+7 −0
Original line number Diff line number Diff line
@@ -17,6 +17,7 @@ 
#include "bpf_skel/off_cpu.skel.h"



#define MAX_STACKS  32

#define MAX_PROC  4096

/* we don't need actual timestamp, just want to put the samples at last */

#define OFF_CPU_TIMESTAMP  (~0ull << 32)
@@ -164,10 +165,16 @@ int off_cpu_prepare(struct evlist *evlist, struct target *target, 


			ntasks++;

		}



		if (ntasks < MAX_PROC)

			ntasks = MAX_PROC;



		bpf_map__set_max_entries(skel->maps.task_filter, ntasks);

	} else if (target__has_task(target)) {

		ntasks = perf_thread_map__nr(evlist->core.threads);

		bpf_map__set_max_entries(skel->maps.task_filter, ntasks);

	} else if (target__none(target)) {

		bpf_map__set_max_entries(skel->maps.task_filter, MAX_PROC);

	}



	if (evlist__first(evlist)->cgrp) {

tools/perf/util/bpf_skel/off_cpu.bpf.c

+30 −0
Original line number Diff line number Diff line
@@ -12,6 +12,9 @@ 
#define TASK_INTERRUPTIBLE	0x0001

#define TASK_UNINTERRUPTIBLE	0x0002



/* create a new thread */

#define CLONE_THREAD  0x10000



#define MAX_STACKS   32

#define MAX_ENTRIES  102400
@@ -220,6 +223,33 @@ static int off_cpu_stat(u64 *ctx, struct task_struct *prev, 
	return 0;

}



SEC("tp_btf/task_newtask")

int on_newtask(u64 *ctx)

{

	struct task_struct *task;

	u64 clone_flags;

	u32 pid;

	u8 val = 1;



	if (!uses_tgid)

		return 0;



	task = (struct task_struct *)bpf_get_current_task();



	pid = BPF_CORE_READ(task, tgid);

	if (!bpf_map_lookup_elem(&task_filter, &pid))

		return 0;



	task = (struct task_struct *)ctx[0];

	clone_flags = ctx[1];



	pid = task->tgid;

	if (!(clone_flags & CLONE_THREAD))

		bpf_map_update_elem(&task_filter, &pid, &val, BPF_NOEXIST);



	return 0;

}



SEC("tp_btf/sched_switch")

int on_switch(u64 *ctx)

{