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Subject[PATCH 5/6] perf offcpu: Track child processes
Date
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: Namhyung Kim <namhyung@kernel.org>
---
tools/perf/util/bpf_off_cpu.c | 7 ++++++
tools/perf/util/bpf_skel/off_cpu.bpf.c | 30 ++++++++++++++++++++++++++
2 files changed, 37 insertions(+)

diff --git a/tools/perf/util/bpf_off_cpu.c b/tools/perf/util/bpf_off_cpu.c
index f7ee0c7a53f0..c257813e674e 100644
--- a/tools/perf/util/bpf_off_cpu.c
+++ b/tools/perf/util/bpf_off_cpu.c
@@ -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) {
diff --git a/tools/perf/util/bpf_skel/off_cpu.bpf.c b/tools/perf/util/bpf_skel/off_cpu.bpf.c
index 143a8b7acf87..c4ba2bcf179f 100644
--- a/tools/perf/util/bpf_skel/off_cpu.bpf.c
+++ b/tools/perf/util/bpf_skel/off_cpu.bpf.c
@@ -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)
{
--
2.37.0.rc0.161.g10f37bed90-goog
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