[PATCH v5] perf sched timehist: Add pre-migration wait time option

From: Madadi Vineeth Reddy
Date: Thu Oct 03 2024 - 15:03:19 EST

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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

The sched:sched_waking event is used to capture the wakeup time,
as it aligns with the existing code and only introduces a negligible
time difference.

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)
--------------- ------ ------------------------------ --------- --------- --------- ---------
38456.720806 [0001] schbench[28634/28574] 4.917 4.768 1.004 0.000
38456.720810 [0001] rcu_preempt[18] 3.919 0.003 0.004 0.000
38456.721800 [0006] schbench[28779/28574] 23.465 23.465 1.999 0.000
38456.722800 [0002] schbench[28773/28574] 60.371 60.237 3.955 60.197
38456.722806 [0001] schbench[28634/28574] 0.004 0.004 1.996 0.000
38456.722811 [0001] rcu_preempt[18] 1.996 0.005 0.005 0.000
38456.723800 [0000] schbench[28833/28574] 4.000 4.000 3.999 0.000
38456.723800 [0004] schbench[28762/28574] 42.951 42.839 3.999 39.867
38456.723802 [0007] schbench[28812/28574] 43.947 43.817 3.999 40.866
38456.723804 [0001] schbench[28587/28574] 7.935 7.822 0.993 0.000

Signed-off-by: Madadi Vineeth Reddy <vineethr@xxxxxxxxxxxxx>

---
Changes in v5:
- Update the ASCII diagram to include dt_pre_mig. (Namhyung Kim)

Changes in v4:
- Remove the redundant check for r->ready_to_run and r->migrated. (Namhyung Kim)
- Rebase against perf-tools-next commit 5873de90315a ("perf/test: perf test
86 fails on s390")

Changes in v3:
- Use the sched:sched_waking event to calculate the wakeup time. (Namhyung Kim)
- Rebase against perf-tools-next commit 80f192724e31 ("perf tests: Add more
topdown events regroup tests")

Changes in v2:
- Use timehist_sched_wakeup_event() to get the sched_wakeup time. (Namhyung Kim)
- Rebase against perf-tools-next commit b38c49d8296b ("perf/test: Speed up test
case perf annotate basic tests")

tools/perf/Documentation/perf-sched.txt | 8 ++
tools/perf/builtin-sched.c | 100 +++++++++++++++---------
2 files changed, 69 insertions(+), 39 deletions(-)

diff --git a/tools/perf/Documentation/perf-sched.txt b/tools/perf/Documentation/perf-sched.txt
index 3db64954a267..6dbbddb6464d 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 sched_wakeup and migrate_task is the pre-migration wait
+ time.
+
OPTIONS for 'perf sched replay'
------------------------------

diff --git a/tools/perf/builtin-sched.c b/tools/perf/builtin-sched.c
index fdf979aaf275..a2fdb1458ba4 100644
--- a/tools/perf/builtin-sched.c
+++ b/tools/perf/builtin-sched.c
@@ -225,6 +225,7 @@ struct perf_sched {
bool show_wakeups;
bool show_next;
bool show_migrations;
+ bool pre_migrations;
bool show_state;
bool show_prio;
u64 skipped_samples;
@@ -244,7 +245,9 @@ 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 migrated; /* time when a thread is migrated */

struct stats run_stats;
u64 total_run_time;
@@ -252,6 +255,7 @@ struct thread_runtime {
u64 total_iowait_time;
u64 total_preempt_time;
u64 total_delay_time;
+ u64 total_pre_mig_time;

char last_state;

@@ -2073,14 +2077,15 @@ 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");
@@ -2095,17 +2100,15 @@ 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");

@@ -2117,15 +2120,15 @@ 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);
@@ -2180,6 +2183,8 @@ 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);
@@ -2217,18 +2222,21 @@ static void timehist_print_sample(struct perf_sched *sched,
* last_time = time of last sched change event for current task
* (i.e, time process was last scheduled out)
* ready_to_run = time of wakeup for current task
+ * migrated = time of task migration to another CPU
*
- * -----|------------|------------|------------|------
- * last ready tprev t
+ * -----|-------------|-------------|-------------|-------------|-----
+ * last ready migrated tprev t
* time to run
*
- * |-------- dt_wait --------|
- * |- dt_delay -|-- dt_run --|
+ * |---------------- dt_wait ----------------|
+ * |--------- dt_delay ---------|-- dt_run --|
+ * |- dt_pre_mig -|
*
- * dt_run = run time of current task
- * dt_wait = time between last schedule out event for task and tprev
- * represents time spent off the cpu
- * dt_delay = time between wakeup and schedule-in of task
+ * dt_run = run time of current task
+ * dt_wait = time between last schedule out event for task and tprev
+ * represents time spent off the cpu
+ * dt_delay = time between wakeup and schedule-in of task
+ * dt_pre_mig = time between wakeup and migration to another CPU
*/

static void timehist_update_runtime_stats(struct thread_runtime *r,
@@ -2239,6 +2247,7 @@ 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;
@@ -2247,6 +2256,9 @@ 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->migrated > r->ready_to_run) && (r->migrated < tprev))
+ r->dt_pre_mig = r->migrated - r->ready_to_run;
}

if (r->last_time > tprev)
@@ -2270,6 +2282,7 @@ 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,
@@ -2684,8 +2697,14 @@ 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;
}
@@ -2836,11 +2855,13 @@ 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 and migrated time */
if (state == 'R')
tr->ready_to_run = t;
else
tr->ready_to_run = 0;
+
+ tr->migrated = 0;
}

evsel__save_time(evsel, sample->time, sample->cpu);
@@ -3280,8 +3301,8 @@ 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->show_migrations || sched->pre_migrations) &&
+ perf_session__set_tracepoints_handlers(session, migrate_handlers))
goto out;

/* pre-allocate struct for per-CPU idle stats */
@@ -3823,6 +3844,7 @@ 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)
};

--
2.43.2

Next message: Florian Fainelli: "Re: [PATCH net] net: phy: bcm84881: Fix some error handling paths"
Previous message: Christophe JAILLET: "[PATCH net] net: ethernet: adi: adin1110: Fix some error handling path in adin1110_read_fifo()"
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