Re: [PATCH v4] perf sched timehist: Add pre-migration wait time option
From: Namhyung Kim
Date: Thu Oct 03 2024 - 12:58:58 EST
On Thu, Oct 03, 2024 at 08:29:14AM +0530, Madadi Vineeth Reddy wrote:
> 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 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 | 81 +++++++++++++++----------
> 2 files changed, 58 insertions(+), 31 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..6dbc2eee69f7 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);
> @@ -2239,6 +2244,7 @@ static void timehist_update_runtime_stats(struct thread_runtime *r,
One last thing, please update the ASCII art in the function comment on
timehist_update_runtime_stats() to contain dt_pre_mig as well.
Thanks,
Namhyung
> 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 +2253,9 @@ 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 +2279,7 @@ 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 +2694,14 @@ 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 +2852,13 @@ 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 +3298,8 @@ 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 +3841,7 @@ 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
>