Commit b44d6653 authored by Namhyung Kim's avatar Namhyung Kim
Browse files

perf lock contention: Account contending locks too 



Currently it accounts the contention using delta between timestamps in
lock:contention_begin and lock:contention_end tracepoints.  But it means
the lock should see the both events during the monitoring period.

Actually there are 4 cases that happen with the monitoring:

                monitoring period
            /                       \
            |                       |
 1:  B------+-----------------------+--------E
 2:    B----+-------------E         |
 3:         |           B-----------+----E
 4:         |     B-------------E   |
            |                       |
            t0                      t1

where B and E mean contention BEGIN and END, respectively.  So it only
accounts the case 4 for now.  It seems there's no way to handle the case
1.  The case 2 might be handled if it saved the timestamp (t0), but it
lacks the information from the B notably the flags which shows the lock
types.  Also it could be a nested lock which it currently ignores.  So
I think we should ignore the case 2.

However we can handle the case 3 if we save the timestamp (t1) at the
end of the period.  And then it can iterate the map entries in the
userspace and update the lock stat accordinly.

Signed-off-by: default avatarNamhyung Kim <namhyung@kernel.org>
Reviewed-by: default avatarIan Rogers <irogers@google.com>
Reviwed-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
Cc: Song Liu <song@kernel.org>
Cc: bpf@vger.kernel.org
Link: https://lore.kernel.org/r/20240228053335.312776-1-namhyung@kernel.org
parent 97b6b4ac

tools/perf/util/bpf_lock_contention.c

+120 −0
Original line number Diff line number Diff line
@@ -179,6 +179,123 @@ int lock_contention_prepare(struct lock_contention *con) 
	return 0;

}



/*

 * Run the BPF program directly using BPF_PROG_TEST_RUN to update the end

 * timestamp in ktime so that it can calculate delta easily.

 */

static void mark_end_timestamp(void)

{

	DECLARE_LIBBPF_OPTS(bpf_test_run_opts, opts,

		.flags = BPF_F_TEST_RUN_ON_CPU,

	);

	int prog_fd = bpf_program__fd(skel->progs.end_timestamp);



	bpf_prog_test_run_opts(prog_fd, &opts);

}



static void update_lock_stat(int map_fd, int pid, u64 end_ts,

			     enum lock_aggr_mode aggr_mode,

			     struct tstamp_data *ts_data)

{

	u64 delta;

	struct contention_key stat_key = {};

	struct contention_data stat_data;



	if (ts_data->timestamp >= end_ts)

		return;



	delta = end_ts - ts_data->timestamp;



	switch (aggr_mode) {

	case LOCK_AGGR_CALLER:

		stat_key.stack_id = ts_data->stack_id;

		break;

	case LOCK_AGGR_TASK:

		stat_key.pid = pid;

		break;

	case LOCK_AGGR_ADDR:

		stat_key.lock_addr_or_cgroup = ts_data->lock;

		break;

	case LOCK_AGGR_CGROUP:

		/* TODO */

		return;

	default:

		return;

	}



	if (bpf_map_lookup_elem(map_fd, &stat_key, &stat_data) < 0)

		return;



	stat_data.total_time += delta;

	stat_data.count++;



	if (delta > stat_data.max_time)

		stat_data.max_time = delta;

	if (delta < stat_data.min_time)

		stat_data.min_time = delta;



	bpf_map_update_elem(map_fd, &stat_key, &stat_data, BPF_EXIST);

}



/*

 * Account entries in the tstamp map (which didn't see the corresponding

 * lock:contention_end tracepoint) using end_ts.

 */

static void account_end_timestamp(struct lock_contention *con)

{

	int ts_fd, stat_fd;

	int *prev_key, key;

	u64 end_ts = skel->bss->end_ts;

	int total_cpus;

	enum lock_aggr_mode aggr_mode = con->aggr_mode;

	struct tstamp_data ts_data, *cpu_data;



	/* Iterate per-task tstamp map (key = TID) */

	ts_fd = bpf_map__fd(skel->maps.tstamp);

	stat_fd = bpf_map__fd(skel->maps.lock_stat);



	prev_key = NULL;

	while (!bpf_map_get_next_key(ts_fd, prev_key, &key)) {

		if (bpf_map_lookup_elem(ts_fd, &key, &ts_data) == 0) {

			int pid = key;



			if (aggr_mode == LOCK_AGGR_TASK && con->owner)

				pid = ts_data.flags;



			update_lock_stat(stat_fd, pid, end_ts, aggr_mode,

					 &ts_data);

		}



		prev_key = &key;

	}



	/* Now it'll check per-cpu tstamp map which doesn't have TID. */

	if (aggr_mode == LOCK_AGGR_TASK || aggr_mode == LOCK_AGGR_CGROUP)

		return;



	total_cpus = cpu__max_cpu().cpu;

	ts_fd = bpf_map__fd(skel->maps.tstamp_cpu);



	cpu_data = calloc(total_cpus, sizeof(*cpu_data));

	if (cpu_data == NULL)

		return;



	prev_key = NULL;

	while (!bpf_map_get_next_key(ts_fd, prev_key, &key)) {

		if (bpf_map_lookup_elem(ts_fd, &key, cpu_data) < 0)

			goto next;



		for (int i = 0; i < total_cpus; i++) {

			update_lock_stat(stat_fd, -1, end_ts, aggr_mode,

					 &cpu_data[i]);

		}



next:

		prev_key = &key;

	}

	free(cpu_data);

}



int lock_contention_start(void)

{

	skel->bss->enabled = 1;
@@ -188,6 +305,7 @@ int lock_contention_start(void) 
int lock_contention_stop(void)

{

	skel->bss->enabled = 0;

	mark_end_timestamp();

	return 0;

}
@@ -301,6 +419,8 @@ int lock_contention_read(struct lock_contention *con) 
	if (stack_trace == NULL)

		return -1;



	account_end_timestamp(con);



	if (con->aggr_mode == LOCK_AGGR_TASK) {

		struct thread *idle = __machine__findnew_thread(machine,

								/*pid=*/0,

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

+9 −7
Original line number Diff line number Diff line
@@ -19,13 +19,6 @@ 
#define LCB_F_PERCPU	(1U << 4)

#define LCB_F_MUTEX	(1U << 5)



struct tstamp_data {

	__u64 timestamp;

	__u64 lock;

	__u32 flags;

	__s32 stack_id;

};



/* callstack storage  */

struct {

	__uint(type, BPF_MAP_TYPE_STACK_TRACE);
@@ -140,6 +133,8 @@ int perf_subsys_id = -1; 
/* determine the key of lock stat */

int aggr_mode;



__u64 end_ts;



/* error stat */

int task_fail;

int stack_fail;
@@ -559,4 +554,11 @@ int BPF_PROG(collect_lock_syms) 
	return 0;

}



SEC("raw_tp/bpf_test_finish")

int BPF_PROG(end_timestamp)

{

	end_ts = bpf_ktime_get_ns();

	return 0;

}



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

tools/perf/util/bpf_skel/lock_data.h

+7 −0
Original line number Diff line number Diff line
@@ -3,6 +3,13 @@ 
#ifndef UTIL_BPF_SKEL_LOCK_DATA_H

#define UTIL_BPF_SKEL_LOCK_DATA_H



struct tstamp_data {

	u64 timestamp;

	u64 lock;

	u32 flags;

	u32 stack_id;

};



struct contention_key {

	u32 stack_id;

	u32 pid;