Re: [PATCH v3 0/7] sched: support schedstats for RT sched class

Peter Zijlstra
2021-08-31T10:44:57Z

On Tue, Aug 31, 2021 at 12:08:15PM +0200, Peter Zijlstra wrote:
> On Tue, Aug 24, 2021 at 11:29:39AM +0000, Yafang Shao wrote:

> > After the patchset, schestats are orgnized as follows,
> > struct task_struct {
> > ...
> > struct sched_statistics statistics;
> > ...
> > struct sched_entity *se;
> > struct sched_rt_entity *rt;
> > ...
> > };
> >
> > struct task_group { |---> stats[0] : of CPU0
> > ... |
> > struct sched_statistics **stats; --|---> stats[1] : of CPU1
> > ... |
> > |---> stats[n] : of CPUn
> > #ifdef CONFIG_FAIR_GROUP_SCHED
> > struct sched_entity **se;
> > #endif
> > #ifdef CONFIG_RT_GROUP_SCHED
> > struct sched_rt_entity **rt_se;
> > #endif
> > ...
> > };
>
> Yeah, this seems to give a terrible mess, let me see if I can come up
> with anything less horrible.

Here, isn't this *MUCH* saner ?

--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -521,7 +521,7 @@ struct sched_statistics {
u64 nr_wakeups_passive;
u64 nr_wakeups_idle;
#endif
-};
+} ____cacheline_aligned;

struct sched_entity {
/* For load-balancing: */
@@ -537,8 +537,6 @@ struct sched_entity {

u64 nr_migrations;

- struct sched_statistics statistics;
-
#ifdef CONFIG_FAIR_GROUP_SCHED
int depth;
struct sched_entity *parent;
@@ -802,6 +800,8 @@ struct task_struct {
struct uclamp_se uclamp[UCLAMP_CNT];
#endif

+ struct sched_statistics stats;
+
#ifdef CONFIG_PREEMPT_NOTIFIERS
/* List of struct preempt_notifier: */
struct hlist_head preempt_notifiers;
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3489,11 +3489,11 @@ ttwu_stat(struct task_struct *p, int cpu
#ifdef CONFIG_SMP
if (cpu == rq->cpu) {
__schedstat_inc(rq->ttwu_local);
- __schedstat_inc(p->se.statistics.nr_wakeups_local);
+ __schedstat_inc(p->stats.nr_wakeups_local);
} else {
struct sched_domain *sd;

- __schedstat_inc(p->se.statistics.nr_wakeups_remote);
+ __schedstat_inc(p->stats.nr_wakeups_remote);
rcu_read_lock();
for_each_domain(rq->cpu, sd) {
if (cpumask_test_cpu(cpu, sched_domain_span(sd))) {
@@ -3505,14 +3505,14 @@ ttwu_stat(struct task_struct *p, int cpu
}

if (wake_flags & WF_MIGRATED)
- __schedstat_inc(p->se.statistics.nr_wakeups_migrate);
+ __schedstat_inc(p->stats.nr_wakeups_migrate);
#endif /* CONFIG_SMP */

__schedstat_inc(rq->ttwu_count);
- __schedstat_inc(p->se.statistics.nr_wakeups);
+ __schedstat_inc(p->stats.nr_wakeups);

if (wake_flags & WF_SYNC)
- __schedstat_inc(p->se.statistics.nr_wakeups_sync);
+ __schedstat_inc(p->stats.nr_wakeups_sync);
}

/*
@@ -4196,7 +4196,7 @@ static void __sched_fork(unsigned long c

#ifdef CONFIG_SCHEDSTATS
/* Even if schedstat is disabled, there should not be garbage */
- memset(&p->se.statistics, 0, sizeof(p->se.statistics));
+ memset(&p->stats, 0, sizeof(p->stats));
#endif

RB_CLEAR_NODE(&p->dl.rb_node);
@@ -9619,9 +9619,9 @@ void normalize_rt_tasks(void)
continue;

p->se.exec_start = 0;
- schedstat_set(p->se.statistics.wait_start, 0);
- schedstat_set(p->se.statistics.sleep_start, 0);
- schedstat_set(p->se.statistics.block_start, 0);
+ schedstat_set(p->stats.wait_start, 0);
+ schedstat_set(p->stats.sleep_start, 0);
+ schedstat_set(p->stats.block_start, 0);

if (!dl_task(p) && !rt_task(p)) {
/*
@@ -10467,7 +10467,7 @@ static int cpu_cfs_stat_show(struct seq_
int i;

for_each_possible_cpu(i)
- ws += schedstat_val(tg->se[i]->statistics.wait_sum);
+ ws += schedstat_val(tg->stats[i]->wait_sum);

seq_printf(sf, "wait_sum %llu\n", ws);
}
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1265,8 +1265,8 @@ static void update_curr_dl(struct rq *rq
return;
}

- schedstat_set(curr->se.statistics.exec_max,
- max(curr->se.statistics.exec_max, delta_exec));
+ schedstat_set(curr->stats.exec_max,
+ max(curr->stats.exec_max, delta_exec));

curr->se.sum_exec_runtime += delta_exec;
account_group_exec_runtime(curr, delta_exec);
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -819,6 +819,21 @@ static void update_tg_load_avg(struct cf
}
#endif /* CONFIG_SMP */

+struct sched_entity_stats {
+ struct sched_entity se;
+ struct sched_statistics stats;
+} __no_randomize_layout;
+
+static inline struct sched_statistics *
+__schedstats_from_se(struct sched_entity *se)
+{
+#ifdef CONFIG_FAIR_GROUP_SCHED
+ if (!entity_is_task(se))
+ return &container_of(se, struct sched_entity_stats, se)->stats;
+#endif
+ return &task_of(se)->stats;
+}
+
/*
* Update the current task's runtime statistics.
*/
@@ -837,8 +852,10 @@ static void update_curr(struct cfs_rq *c

curr->exec_start = now;

- schedstat_set(curr->statistics.exec_max,
- max(delta_exec, curr->statistics.exec_max));
+ if (schedstat_enabled()) {
+ struct sched_statistics *stats = __schedstats_from_se(curr);
+ __schedstat_set(stats->exec_max, max(delta_exec, stats->exec_max));
+ }

curr->sum_exec_runtime += delta_exec;
schedstat_add(cfs_rq->exec_clock, delta_exec);
@@ -866,39 +883,45 @@ static inline void
update_stats_wait_start(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
u64 wait_start, prev_wait_start;
+ struct sched_statistics *stats;

if (!schedstat_enabled())
return;

+ stats = __schedstats_from_se(se);
+
wait_start = rq_clock(rq_of(cfs_rq));
- prev_wait_start = schedstat_val(se->statistics.wait_start);
+ prev_wait_start = schedstat_val(stats->wait_start);

if (entity_is_task(se) && task_on_rq_migrating(task_of(se)) &&
likely(wait_start > prev_wait_start))
wait_start -= prev_wait_start;

- __schedstat_set(se->statistics.wait_start, wait_start);
+ __schedstat_set(stats->wait_start, wait_start);
}

static inline void
update_stats_wait_end(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
- struct task_struct *p;
+ struct sched_statistics *stats;
+ struct task_struct *p = NULL;
u64 delta;

if (!schedstat_enabled())
return;

+ stats = __schedstats_from_se(se);
+
/*
* When the sched_schedstat changes from 0 to 1, some sched se
* maybe already in the runqueue, the se->statistics.wait_start
* will be 0.So it will let the delta wrong. We need to avoid this
* scenario.
*/
- if (unlikely(!schedstat_val(se->statistics.wait_start)))
+ if (unlikely(!schedstat_val(stats->wait_start)))
return;

- delta = rq_clock(rq_of(cfs_rq)) - schedstat_val(se->statistics.wait_start);
+ delta = rq_clock(rq_of(cfs_rq)) - schedstat_val(stats->wait_start);

if (entity_is_task(se)) {
p = task_of(se);
@@ -908,30 +931,33 @@ update_stats_wait_end(struct cfs_rq *cfs
* time stamp can be adjusted to accumulate wait time
* prior to migration.
*/
- __schedstat_set(se->statistics.wait_start, delta);
+ __schedstat_set(stats->wait_start, delta);
return;
}
trace_sched_stat_wait(p, delta);
}

- __schedstat_set(se->statistics.wait_max,
- max(schedstat_val(se->statistics.wait_max), delta));
- __schedstat_inc(se->statistics.wait_count);
- __schedstat_add(se->statistics.wait_sum, delta);
- __schedstat_set(se->statistics.wait_start, 0);
+ __schedstat_set(stats->wait_max,
+ max(schedstat_val(stats->wait_max), delta));
+ __schedstat_inc(stats->wait_count);
+ __schedstat_add(stats->wait_sum, delta);
+ __schedstat_set(stats->wait_start, 0);
}

static inline void
update_stats_enqueue_sleeper(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
+ struct sched_statistics *stats;
struct task_struct *tsk = NULL;
u64 sleep_start, block_start;

if (!schedstat_enabled())
return;

- sleep_start = schedstat_val(se->statistics.sleep_start);
- block_start = schedstat_val(se->statistics.block_start);
+ stats = __schedstats_from_se(se);
+
+ sleep_start = schedstat_val(stats->sleep_start);
+ block_start = schedstat_val(stats->block_start);

if (entity_is_task(se))
tsk = task_of(se);
@@ -942,11 +968,11 @@ update_stats_enqueue_sleeper(struct cfs_
if ((s64)delta < 0)
delta = 0;

- if (unlikely(delta > schedstat_val(se->statistics.sleep_max)))
- __schedstat_set(se->statistics.sleep_max, delta);
+ if (unlikely(delta > schedstat_val(stats->sleep_max)))
+ __schedstat_set(stats->sleep_max, delta);

- __schedstat_set(se->statistics.sleep_start, 0);
- __schedstat_add(se->statistics.sum_sleep_runtime, delta);
+ __schedstat_set(stats->sleep_start, 0);
+ __schedstat_add(stats->sum_sleep_runtime, delta);

if (tsk) {
account_scheduler_latency(tsk, delta >> 10, 1);
@@ -959,16 +985,16 @@ update_stats_enqueue_sleeper(struct cfs_
if ((s64)delta < 0)
delta = 0;

- if (unlikely(delta > schedstat_val(se->statistics.block_max)))
- __schedstat_set(se->statistics.block_max, delta);
+ if (unlikely(delta > schedstat_val(stats->block_max)))
+ __schedstat_set(stats->block_max, delta);

- __schedstat_set(se->statistics.block_start, 0);
- __schedstat_add(se->statistics.sum_sleep_runtime, delta);
+ __schedstat_set(stats->block_start, 0);
+ __schedstat_add(stats->sum_sleep_runtime, delta);

if (tsk) {
if (tsk->in_iowait) {
- __schedstat_add(se->statistics.iowait_sum, delta);
- __schedstat_inc(se->statistics.iowait_count);
+ __schedstat_add(stats->iowait_sum, delta);
+ __schedstat_inc(stats->iowait_count);
trace_sched_stat_iowait(tsk, delta);
}

@@ -1030,10 +1056,10 @@ update_stats_dequeue(struct cfs_rq *cfs_
/* XXX racy against TTWU */
state = READ_ONCE(tsk->__state);
if (state & TASK_INTERRUPTIBLE)
- __schedstat_set(se->statistics.sleep_start,
+ __schedstat_set(tsk->stats.sleep_start,
rq_clock(rq_of(cfs_rq)));
if (state & TASK_UNINTERRUPTIBLE)
- __schedstat_set(se->statistics.block_start,
+ __schedstat_set(tsk->stats.block_start,
rq_clock(rq_of(cfs_rq)));
}
}
@@ -4502,9 +4528,10 @@ set_next_entity(struct cfs_rq *cfs_rq, s
*/
if (schedstat_enabled() &&
rq_of(cfs_rq)->cfs.load.weight >= 2*se->load.weight) {
- __schedstat_set(se->statistics.slice_max,
- max((u64)schedstat_val(se->statistics.slice_max),
- se->sum_exec_runtime - se->prev_sum_exec_runtime));
+ struct sched_statistics *stats = __schedstats_from_se(se);
+ __schedstat_set(stats->slice_max,
+ max((u64)stats->slice_max,
+ se->sum_exec_runtime - se->prev_sum_exec_runtime));
}

se->prev_sum_exec_runtime = se->sum_exec_runtime;
@@ -5993,12 +6020,12 @@ static int wake_affine(struct sched_doma
if (sched_feat(WA_WEIGHT) && target == nr_cpumask_bits)
target = wake_affine_weight(sd, p, this_cpu, prev_cpu, sync);

- schedstat_inc(p->se.statistics.nr_wakeups_affine_attempts);
+ schedstat_inc(p->stats.nr_wakeups_affine_attempts);
if (target == nr_cpumask_bits)
return prev_cpu;

schedstat_inc(sd->ttwu_move_affine);
- schedstat_inc(p->se.statistics.nr_wakeups_affine);
+ schedstat_inc(p->stats.nr_wakeups_affine);
return target;
}

@@ -7802,7 +7829,7 @@ int can_migrate_task(struct task_struct
if (!cpumask_test_cpu(env->dst_cpu, p->cpus_ptr)) {
int cpu;

- schedstat_inc(p->se.statistics.nr_failed_migrations_affine);
+ schedstat_inc(p->stats.nr_failed_migrations_affine);

env->flags |= LBF_SOME_PINNED;

@@ -7836,7 +7863,7 @@ int can_migrate_task(struct task_struct
env->flags &= ~LBF_ALL_PINNED;

if (task_running(env->src_rq, p)) {
- schedstat_inc(p->se.statistics.nr_failed_migrations_running);
+ schedstat_inc(p->stats.nr_failed_migrations_running);
return 0;
}

@@ -7858,12 +7885,12 @@ int can_migrate_task(struct task_struct
env->sd->nr_balance_failed > env->sd->cache_nice_tries) {
if (tsk_cache_hot == 1) {
schedstat_inc(env->sd->lb_hot_gained[env->idle]);
- schedstat_inc(p->se.statistics.nr_forced_migrations);
+ schedstat_inc(p->stats.nr_forced_migrations);
}
return 1;
}

- schedstat_inc(p->se.statistics.nr_failed_migrations_hot);
+ schedstat_inc(p->stats.nr_failed_migrations_hot);
return 0;
}

@@ -11390,7 +11417,7 @@ int alloc_fair_sched_group(struct task_g
if (!cfs_rq)
goto err;

- se = kzalloc_node(sizeof(struct sched_entity),
+ se = kzalloc_node(sizeof(struct sched_entity_stats),
GFP_KERNEL, cpu_to_node(i));
if (!se)
goto err_free_rq;
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1009,8 +1009,8 @@ static void update_curr_rt(struct rq *rq
if (unlikely((s64)delta_exec <= 0))
return;

- schedstat_set(curr->se.statistics.exec_max,
- max(curr->se.statistics.exec_max, delta_exec));
+ schedstat_set(curr->stats.exec_max,
+ max(curr->stats.exec_max, delta_exec));

curr->se.sum_exec_runtime += delta_exec;
account_group_exec_runtime(curr, delta_exec);
--- a/kernel/sched/stats.h
+++ b/kernel/sched/stats.h
@@ -41,6 +41,7 @@ rq_sched_info_dequeue(struct rq *rq, uns
#define schedstat_val_or_zero(var) ((schedstat_enabled()) ? (var) : 0)

#else /* !CONFIG_SCHEDSTATS: */
+
static inline void rq_sched_info_arrive (struct rq *rq, unsigned long long delta) { }
static inline void rq_sched_info_dequeue(struct rq *rq, unsigned long long delta) { }
static inline void rq_sched_info_depart (struct rq *rq, unsigned long long delta) { }
@@ -53,6 +54,7 @@ static inline void rq_sched_info_depart
# define schedstat_set(var, val) do { } while (0)
# define schedstat_val(var) 0
# define schedstat_val_or_zero(var) 0
+
#endif /* CONFIG_SCHEDSTATS */

#ifdef CONFIG_PSI
--- a/kernel/sched/stop_task.c
+++ b/kernel/sched/stop_task.c
@@ -78,8 +78,8 @@ static void put_prev_task_stop(struct rq
if (unlikely((s64)delta_exec < 0))
delta_exec = 0;

- schedstat_set(curr->se.statistics.exec_max,
- max(curr->se.statistics.exec_max, delta_exec));
+ schedstat_set(curr->stats.exec_max,
+ max(curr->stats.exec_max, delta_exec));

curr->se.sum_exec_runtime += delta_exec;
account_group_exec_runtime(curr, delta_exec);