Commit b36888f7 authored by Namhyung Kim's avatar Namhyung Kim Committed by Arnaldo Carvalho de Melo
Browse files

perf record: Handle argument change in sched_switch 



Recently sched_switch tracepoint added a new argument for prev_state,
but it's hard to handle the change in a BPF program.  Instead, we can
check the function prototype in BTF before loading the program.

Signed-off-by: default avatarNamhyung Kim <namhyung@kernel.org>
Acked-by: default avatarIan Rogers <irogers@google.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Blake Jones <blakejones@google.com>
Cc: Hao Luo <haoluo@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/20220518224725.742882-5-namhyung@kernel.org


Signed-off-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
parent 10742d0c

tools/perf/util/bpf_off_cpu.c

+28 −0
Original line number Diff line number Diff line
@@ -89,6 +89,33 @@ static void off_cpu_finish(void *arg __maybe_unused) 
	off_cpu_bpf__destroy(skel);

}



/* v5.18 kernel added prev_state arg, so it needs to check the signature */

static void check_sched_switch_args(void)

{

	const struct btf *btf = bpf_object__btf(skel->obj);

	const struct btf_type *t1, *t2, *t3;

	u32 type_id;



	type_id = btf__find_by_name_kind(btf, "bpf_trace_sched_switch",

					 BTF_KIND_TYPEDEF);

	if ((s32)type_id < 0)

		return;



	t1 = btf__type_by_id(btf, type_id);

	if (t1 == NULL)

		return;



	t2 = btf__type_by_id(btf, t1->type);

	if (t2 == NULL || !btf_is_ptr(t2))

		return;



	t3 = btf__type_by_id(btf, t2->type);

	if (t3 && btf_is_func_proto(t3) && btf_vlen(t3) == 4) {

		/* new format: pass prev_state as 4th arg */

		skel->rodata->has_prev_state = true;

	}

}



int off_cpu_prepare(struct evlist *evlist, struct target *target)

{

	int err, fd, i;
@@ -117,6 +144,7 @@ int off_cpu_prepare(struct evlist *evlist, struct target *target) 
	}



	set_max_rlimit();

	check_sched_switch_args();



	err = off_cpu_bpf__load(skel);

	if (err) {

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

+24 −11
Original line number Diff line number Diff line
@@ -72,6 +72,8 @@ int enabled = 0; 
int has_cpu = 0;

int has_task = 0;



const volatile bool has_prev_state = false;



/*

 * Old kernel used to call it task_struct->state and now it's '__state'.

 * Use BPF CO-RE "ignored suffix rule" to deal with it like below:
@@ -121,22 +123,13 @@ static inline int can_record(struct task_struct *t, int state) 
	return 1;

}



SEC("tp_btf/sched_switch")

int on_switch(u64 *ctx)

static int off_cpu_stat(u64 *ctx, struct task_struct *prev,

			struct task_struct *next, int state)

{

	__u64 ts;

	int state;

	__u32 stack_id;

	struct task_struct *prev, *next;

	struct tstamp_data *pelem;



	if (!enabled)

		return 0;



	prev = (struct task_struct *)ctx[1];

	next = (struct task_struct *)ctx[2];

	state = get_task_state(prev);



	ts = bpf_ktime_get_ns();



	if (!can_record(prev, state))
@@ -180,4 +173,24 @@ int on_switch(u64 *ctx) 
	return 0;

}



SEC("tp_btf/sched_switch")

int on_switch(u64 *ctx)

{

	struct task_struct *prev, *next;

	int prev_state;



	if (!enabled)

		return 0;



	prev = (struct task_struct *)ctx[1];

	next = (struct task_struct *)ctx[2];



	if (has_prev_state)

		prev_state = (int)ctx[3];

	else

		prev_state = get_task_state(prev);



	return off_cpu_stat(ctx, prev, next, prev_state);

}



char LICENSE[] SEC("license") = "Dual BSD/GPL";