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* [PATCH] perf sched timehist: Add pre-migration wait time option
@ 2024-09-17  9:15 Madadi Vineeth Reddy
  2024-09-26 23:04 ` Namhyung Kim
  0 siblings, 1 reply; 3+ messages in thread
From: Madadi Vineeth Reddy @ 2024-09-17  9:15 UTC (permalink / raw)
  To: Arnaldo Carvalho de Melo, Namhyung Kim, Ian Rogers, Athira Rajeev,
	Peter Zijlstra, Ingo Molnar, Mark Rutland, Alexander Shishkin,
	Jiri Olsa, Adrian Hunter, Kan Liang, acme, linux-perf-users, LKML
  Cc: Madadi Vineeth Reddy

pre-migration wait time is the time that a task unnecessarily spends
on the runqueue of a CPU but doesn't get switched-in there. In terms
of tracepoints, it is the time between sched:sched_wakeup and
sched:sched_migrate_task.

Let's say a task woke up on CPU2, then it got migrated to CPU4 and
then it's switched-in to CPU4. So, here pre-migration wait time is
time that it was waiting on runqueue of CPU2 after it is woken up.

The general pattern for pre-migration to occur is:
sched:sched_wakeup
sched:sched_migrate_task
sched:sched_switch
So, this option expects sched_wakeup also to be recorded and fails
if attempted to use the option without sched:sched_wakeup tracepoint.

pre-migrations are generally not useful and it increases migrations.
This metric would be helpful in testing patches mainly related to wakeup
and load-balancer code paths as better wakeup logic would choose an
optimal CPU where task would be switched-in and thereby reducing pre-
migrations.

The sample output(s) when -P or --pre-migrations is used:
=================
           time    cpu  task name                       wait time  sch delay   run time  pre-mig time
                        [tid/pid]                          (msec)     (msec)     (msec)     (msec)
--------------- ------  ------------------------------  ---------  ---------  ---------  ---------
  103032.721020 [0000]  perf[47206]                         0.000      0.000      0.000      0.000
  103032.721034 [0000]  migration/0[18]                     0.000      0.003      0.013      0.000
  103032.736716 [0001]  schbench[47229/47207]              10.664      9.231      0.039      9.170
  103032.736719 [0005]  <idle>                              0.000      0.000     15.405      0.000
  103032.736726 [0003]  schbench[47216/47207]              11.251      9.193      0.022      9.126
  103032.736727 [0001]  schbench[47228/47207]              10.752      9.264      0.010      9.169
  103032.736731 [0007]  <idle>                              0.000      0.000     15.314      0.000
  103032.736739 [0008]  <idle>                              0.000      0.000     15.249      0.000
  103032.736742 [0003]  schbench[47257/47207]               9.498      9.184      0.015      9.100

   51370.894024 [0012]  schbench[38775/38770]              21.047     21.047      8.950      0.000
   51370.894024 [0008]  schbench[38781/38770]              39.597     39.448      9.984     39.437
   51370.894025 [0009]  stress-ng-cpu[38743]                7.971      7.971      9.997      0.000

Signed-off-by: Madadi Vineeth Reddy <vineethr@linux.ibm.com>
---
 tools/perf/Documentation/perf-sched.txt |   8 ++
 tools/perf/builtin-sched.c              | 110 +++++++++++++++++-------
 2 files changed, 85 insertions(+), 33 deletions(-)

diff --git a/tools/perf/Documentation/perf-sched.txt b/tools/perf/Documentation/perf-sched.txt
index 3db64954a267..7935499b88b0 100644
--- a/tools/perf/Documentation/perf-sched.txt
+++ b/tools/perf/Documentation/perf-sched.txt
@@ -221,6 +221,14 @@ OPTIONS for 'perf sched timehist'
 	priorities are specified with -: 120-129. A combination of both can also be
 	provided: 0,120-129.
 
+-P::
+--pre-migrations::
+	Show pre-migration wait time. pre-migration wait time is the time spent
+	by a task waiting on a runqueue but not getting the chance to run there
+	and is migrated to a different runqueue where it is finally run. This
+	time between migrate_task and sched_wakeup is the pre-migration wait
+	time. This option is valid only if sched_wakeup tracepoint is recorded.
+
 OPTIONS for 'perf sched replay'
 ------------------------------
 
diff --git a/tools/perf/builtin-sched.c b/tools/perf/builtin-sched.c
index 5981cc51abc8..252e71d83d82 100644
--- a/tools/perf/builtin-sched.c
+++ b/tools/perf/builtin-sched.c
@@ -228,6 +228,7 @@ struct perf_sched {
 	bool		show_wakeups;
 	bool		show_next;
 	bool		show_migrations;
+	bool		pre_migrations;
 	bool		show_state;
 	bool		show_prio;
 	u64		skipped_samples;
@@ -247,7 +248,10 @@ struct thread_runtime {
 	u64 dt_iowait;      /* time between CPU access by iowait (off cpu) */
 	u64 dt_preempt;     /* time between CPU access by preempt (off cpu) */
 	u64 dt_delay;       /* time between wakeup and sched-in */
+	u64 dt_pre_mig;     /* time between migration and wakeup */
 	u64 ready_to_run;   /* time of wakeup */
+	u64 woken;	    /* time when sched_wakeup tracepoint is hit */
+	u64 migrated;	    /* time when a thread is migrated */
 
 	struct stats run_stats;
 	u64 total_run_time;
@@ -255,6 +259,7 @@ struct thread_runtime {
 	u64 total_iowait_time;
 	u64 total_preempt_time;
 	u64 total_delay_time;
+	u64 total_pre_mig_time;
 
 	char last_state;
 
@@ -2083,14 +2088,15 @@ static void timehist_header(struct perf_sched *sched)
 		printf(" ");
 	}
 
-	if (sched->show_prio) {
-		printf(" %-*s  %-*s  %9s  %9s  %9s",
-		       comm_width, "task name", MAX_PRIO_STR_LEN, "prio",
-		       "wait time", "sch delay", "run time");
-	} else {
-		printf(" %-*s  %9s  %9s  %9s", comm_width,
-		       "task name", "wait time", "sch delay", "run time");
-	}
+	printf(" %-*s", comm_width, "task name");
+
+	if (sched->show_prio)
+		printf("  %-*s", MAX_PRIO_STR_LEN, "prio");
+
+	printf("  %9s  %9s  %9s", "wait time", "sch delay", "run time");
+
+	if (sched->pre_migrations)
+		printf("  %9s", "pre-mig time");
 
 	if (sched->show_state)
 		printf("  %s", "state");
@@ -2105,17 +2111,15 @@ static void timehist_header(struct perf_sched *sched)
 	if (sched->show_cpu_visual)
 		printf(" %*s ", ncpus, "");
 
-	if (sched->show_prio) {
-		printf(" %-*s  %-*s  %9s  %9s  %9s",
-		       comm_width, "[tid/pid]", MAX_PRIO_STR_LEN, "",
-		       "(msec)", "(msec)", "(msec)");
-	} else {
-		printf(" %-*s  %9s  %9s  %9s", comm_width,
-		       "[tid/pid]", "(msec)", "(msec)", "(msec)");
-	}
+	printf(" %-*s", comm_width, "[tid/pid]");
 
-	if (sched->show_state)
-		printf("  %5s", "");
+	if (sched->show_prio)
+		printf("  %-*s", MAX_PRIO_STR_LEN, "");
+
+	printf("  %9s  %9s  %9s", "(msec)", "(msec)", "(msec)");
+
+	if (sched->pre_migrations)
+		printf("  %9s", "(msec)");
 
 	printf("\n");
 
@@ -2127,15 +2131,15 @@ static void timehist_header(struct perf_sched *sched)
 	if (sched->show_cpu_visual)
 		printf(" %.*s ", ncpus, graph_dotted_line);
 
-	if (sched->show_prio) {
-		printf(" %.*s  %.*s  %.9s  %.9s  %.9s",
-		       comm_width, graph_dotted_line, MAX_PRIO_STR_LEN, graph_dotted_line,
-		       graph_dotted_line, graph_dotted_line, graph_dotted_line);
-	} else {
-		printf(" %.*s  %.9s  %.9s  %.9s", comm_width,
-		       graph_dotted_line, graph_dotted_line, graph_dotted_line,
-		       graph_dotted_line);
-	}
+	printf(" %.*s", comm_width, graph_dotted_line);
+
+	if (sched->show_prio)
+		printf("  %.*s", MAX_PRIO_STR_LEN, graph_dotted_line);
+
+	printf("  %.9s  %.9s  %.9s", graph_dotted_line, graph_dotted_line, graph_dotted_line);
+
+	if (sched->pre_migrations)
+		printf("  %.9s", graph_dotted_line);
 
 	if (sched->show_state)
 		printf("  %.5s", graph_dotted_line);
@@ -2190,6 +2194,8 @@ static void timehist_print_sample(struct perf_sched *sched,
 
 	print_sched_time(tr->dt_delay, 6);
 	print_sched_time(tr->dt_run, 6);
+	if (sched->pre_migrations)
+		print_sched_time(tr->dt_pre_mig, 6);
 
 	if (sched->show_state)
 		printf(" %5c ", thread__tid(thread) == 0 ? 'I' : state);
@@ -2249,6 +2255,7 @@ static void timehist_update_runtime_stats(struct thread_runtime *r,
 	r->dt_iowait  = 0;
 	r->dt_preempt = 0;
 	r->dt_run     = 0;
+	r->dt_pre_mig = 0;
 
 	if (tprev) {
 		r->dt_run = t - tprev;
@@ -2257,6 +2264,11 @@ static void timehist_update_runtime_stats(struct thread_runtime *r,
 				pr_debug("time travel: wakeup time for task > previous sched_switch event\n");
 			else
 				r->dt_delay = tprev - r->ready_to_run;
+
+			if (r->woken && r->migrated) {
+				if ((r->migrated > r->woken) && (r->migrated < tprev))
+					r->dt_pre_mig = r->migrated - r->woken;
+			}
 		}
 
 		if (r->last_time > tprev)
@@ -2280,6 +2292,7 @@ static void timehist_update_runtime_stats(struct thread_runtime *r,
 	r->total_sleep_time   += r->dt_sleep;
 	r->total_iowait_time  += r->dt_iowait;
 	r->total_preempt_time += r->dt_preempt;
+	r->total_pre_mig_time += r->dt_pre_mig;
 }
 
 static bool is_idle_sample(struct perf_sample *sample,
@@ -2579,12 +2592,27 @@ static void timehist_print_wakeup_event(struct perf_sched *sched,
 	printf("\n");
 }
 
-static int timehist_sched_wakeup_ignore(const struct perf_tool *tool __maybe_unused,
+static int timehist_sched_wakeup_consider(const struct perf_tool *tool __maybe_unused,
 					union perf_event *event __maybe_unused,
 					struct evsel *evsel __maybe_unused,
 					struct perf_sample *sample __maybe_unused,
 					struct machine *machine __maybe_unused)
 {
+	struct thread *thread;
+	struct thread_runtime *tr = NULL;
+	const u32 pid = evsel__intval(evsel, sample, "pid");
+
+	thread = machine__findnew_thread(machine, 0, pid);
+	if (thread == NULL)
+		return -1;
+
+	tr = thread__get_runtime(thread);
+	if (tr == NULL)
+		return -1;
+
+	if (tr->woken == 0)
+		tr->woken = sample->time;
+
 	return 0;
 }
 
@@ -2694,8 +2722,14 @@ static int timehist_migrate_task_event(const struct perf_tool *tool,
 
 	tr->migrations++;
 
+	if (tr->migrated == 0)
+		tr->migrated = sample->time;
+
 	/* show migrations if requested */
-	timehist_print_migration_event(sched, evsel, sample, machine, thread);
+	if (sched->show_migrations) {
+		timehist_print_migration_event(sched, evsel, sample,
+							machine, thread);
+	}
 
 	return 0;
 }
@@ -2846,11 +2880,14 @@ static int timehist_sched_change_event(const struct perf_tool *tool,
 		/* last state is used to determine where to account wait time */
 		tr->last_state = state;
 
-		/* sched out event for task so reset ready to run time */
+		/* sched out event for task so reset ready to run time, woken and migrated time */
 		if (state == 'R')
 			tr->ready_to_run = t;
 		else
 			tr->ready_to_run = 0;
+
+		tr->woken = 0;
+		tr->migrated = 0;
 	}
 
 	evsel__save_time(evsel, sample->time, sample->cpu);
@@ -3278,7 +3315,7 @@ static int perf_sched__timehist(struct perf_sched *sched)
 
 	/* prefer sched_waking if it is captured */
 	if (evlist__find_tracepoint_by_name(session->evlist, "sched:sched_waking"))
-		handlers[1].handler = timehist_sched_wakeup_ignore;
+		handlers[1].handler = timehist_sched_wakeup_consider;
 
 	/* setup per-evsel handlers */
 	if (perf_session__set_tracepoints_handlers(session, handlers))
@@ -3290,8 +3327,14 @@ static int perf_sched__timehist(struct perf_sched *sched)
 		goto out;
 	}
 
-	if (sched->show_migrations &&
-	    perf_session__set_tracepoints_handlers(session, migrate_handlers))
+	if (sched->pre_migrations && !evlist__find_tracepoint_by_name(session->evlist,
+									"sched:sched_wakeup")) {
+		pr_err("No sched_wakeup events found. sched_wakeup tracepoint is mandatory for -P option\n");
+		goto out;
+	}
+
+	if ((sched->show_migrations || sched->pre_migrations) &&
+		(perf_session__set_tracepoints_handlers(session, migrate_handlers)))
 		goto out;
 
 	/* pre-allocate struct for per-CPU idle stats */
@@ -3833,6 +3876,7 @@ int cmd_sched(int argc, const char **argv)
 	OPT_BOOLEAN(0, "show-prio", &sched.show_prio, "Show task priority"),
 	OPT_STRING(0, "prio", &sched.prio_str, "prio",
 		   "analyze events only for given task priority(ies)"),
+	OPT_BOOLEAN('P', "pre-migrations", &sched.pre_migrations, "Show pre-migration wait time"),
 	OPT_PARENT(sched_options)
 	};
 
-- 
2.43.1


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2024-09-17  9:15 [PATCH] perf sched timehist: Add pre-migration wait time option Madadi Vineeth Reddy
2024-09-26 23:04 ` Namhyung Kim
2024-10-01  6:03   ` Madadi Vineeth Reddy

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