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Subject[PATCH v2] psi: Remove the redundant psi_task_tick
Date
When the current task in a cgroup is in_memstall, the corresponding groupc
on that cpu is in PSI_MEM_FULL state, so we can exploit that to remove the
redundant psi_task_tick from scheduler_tick to save this periodic cost.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
---
include/linux/psi.h | 1 -
kernel/sched/core.c | 1 -
kernel/sched/psi.c | 49 ++++++++++++++-----------------------------------
kernel/sched/stats.h | 9 ---------
4 files changed, 14 insertions(+), 46 deletions(-)

diff --git a/include/linux/psi.h b/include/linux/psi.h
index 7361023f3fdd..65eb1476ac70 100644
--- a/include/linux/psi.h
+++ b/include/linux/psi.h
@@ -20,7 +20,6 @@ void psi_task_change(struct task_struct *task, int clear, int set);
void psi_task_switch(struct task_struct *prev, struct task_struct *next,
bool sleep);

-void psi_memstall_tick(struct task_struct *task, int cpu);
void psi_memstall_enter(unsigned long *flags);
void psi_memstall_leave(unsigned long *flags);

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 15d2562118d1..31788a9b335b 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4533,7 +4533,6 @@ void scheduler_tick(void)
update_thermal_load_avg(rq_clock_thermal(rq), rq, thermal_pressure);
curr->sched_class->task_tick(rq, curr, 0);
calc_global_load_tick(rq);
- psi_task_tick(rq);

rq_unlock(rq, &rf);

diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index 2293c45d289d..6e46d9eb279b 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -644,8 +644,7 @@ static void poll_timer_fn(struct timer_list *t)
wake_up_interruptible(&group->poll_wait);
}

-static void record_times(struct psi_group_cpu *groupc, int cpu,
- bool memstall_tick)
+static void record_times(struct psi_group_cpu *groupc, int cpu)
{
u32 delta;
u64 now;
@@ -664,23 +663,6 @@ static void record_times(struct psi_group_cpu *groupc, int cpu,
groupc->times[PSI_MEM_SOME] += delta;
if (groupc->state_mask & (1 << PSI_MEM_FULL))
groupc->times[PSI_MEM_FULL] += delta;
- else if (memstall_tick) {
- u32 sample;
- /*
- * Since we care about lost potential, a
- * memstall is FULL when there are no other
- * working tasks, but also when the CPU is
- * actively reclaiming and nothing productive
- * could run even if it were runnable.
- *
- * When the timer tick sees a reclaiming CPU,
- * regardless of runnable tasks, sample a FULL
- * tick (or less if it hasn't been a full tick
- * since the last state change).
- */
- sample = min(delta, (u32)jiffies_to_nsecs(1));
- groupc->times[PSI_MEM_FULL] += sample;
- }
}

if (groupc->state_mask & (1 << PSI_CPU_SOME)) {
@@ -714,7 +696,7 @@ static void psi_group_change(struct psi_group *group, int cpu,
*/
write_seqcount_begin(&groupc->seq);

- record_times(groupc, cpu, false);
+ record_times(groupc, cpu);

for (t = 0, m = clear; m; m &= ~(1 << t), t++) {
if (!(m & (1 << t)))
@@ -738,6 +720,18 @@ static void psi_group_change(struct psi_group *group, int cpu,
if (test_state(groupc->tasks, s))
state_mask |= (1 << s);
}
+
+ /*
+ * Since we care about lost potential, a memstall is FULL
+ * when there are no other working tasks, but also when
+ * the CPU is actively reclaiming and nothing productive
+ * could run even if it were runnable. So when the current
+ * task in a cgroup is in_memstall, the corresponding groupc
+ * on that cpu is in PSI_MEM_FULL state.
+ */
+ if (groupc->tasks[NR_ONCPU] && cpu_curr(cpu)->in_memstall)
+ state_mask |= (1 << PSI_MEM_FULL);
+
groupc->state_mask = state_mask;

write_seqcount_end(&groupc->seq);
@@ -859,21 +853,6 @@ void psi_task_switch(struct task_struct *prev, struct task_struct *next,
}
}

-void psi_memstall_tick(struct task_struct *task, int cpu)
-{
- struct psi_group *group;
- void *iter = NULL;
-
- while ((group = iterate_groups(task, &iter))) {
- struct psi_group_cpu *groupc;
-
- groupc = per_cpu_ptr(group->pcpu, cpu);
- write_seqcount_begin(&groupc->seq);
- record_times(groupc, cpu, true);
- write_seqcount_end(&groupc->seq);
- }
-}
-
/**
* psi_memstall_enter - mark the beginning of a memory stall section
* @flags: flags to handle nested sections
diff --git a/kernel/sched/stats.h b/kernel/sched/stats.h
index 33d0daf83842..9e4e67a94731 100644
--- a/kernel/sched/stats.h
+++ b/kernel/sched/stats.h
@@ -144,14 +144,6 @@ static inline void psi_sched_switch(struct task_struct *prev,
psi_task_switch(prev, next, sleep);
}

-static inline void psi_task_tick(struct rq *rq)
-{
- if (static_branch_likely(&psi_disabled))
- return;
-
- if (unlikely(rq->curr->in_memstall))
- psi_memstall_tick(rq->curr, cpu_of(rq));
-}
#else /* CONFIG_PSI */
static inline void psi_enqueue(struct task_struct *p, bool wakeup) {}
static inline void psi_dequeue(struct task_struct *p, bool sleep) {}
@@ -159,7 +151,6 @@ static inline void psi_ttwu_dequeue(struct task_struct *p) {}
static inline void psi_sched_switch(struct task_struct *prev,
struct task_struct *next,
bool sleep) {}
-static inline void psi_task_tick(struct rq *rq) {}
#endif /* CONFIG_PSI */

#ifdef CONFIG_SCHED_INFO
--
2.11.0
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