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sched: Simplify sched_info_on()

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The situation around sched_info is somewhat complicated, it is used by
sched_stats and delayacct and, indirectly, kvm.

If SCHEDSTATS=Y (but disabled by default) sched_info_on() is
unconditionally true -- this is the case for all distro kernel configs
I checked.

If for some reason SCHEDSTATS=N, but TASK_DELAY_ACCT=Y, then
sched_info_on() can return false when delayacct is disabled,
presumably because there would be no other users left; except kvm is.

Instead of complicating matters further by accurately accounting
sched_stat and kvm state, simply unconditionally enable when
SCHED_INFO=Y, matching the common distro case.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Link: https://lkml.kernel.org/r/20210505111525.121458839@infradead.org
This commit is contained in:
Peter Zijlstra 2021-05-04 22:43:42 +02:00
parent 4e29fb7098
commit c5895d3f06
3 changed files with 12 additions and 36 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

10
include/linux/sched/stat.h
View file

@ -3,6 +3,7 @@
#define _LINUX_SCHED_STAT_H
#include <linux/percpu.h>
#include <linux/kconfig.h>
/*
* Various counters maintained by the scheduler and fork(),
@ -23,14 +24,7 @@ extern unsigned long nr_iowait_cpu(int cpu);
static inline int sched_info_on(void)
{
#ifdef CONFIG_SCHEDSTATS
return 1;
#elif defined(CONFIG_TASK_DELAY_ACCT)
extern int delayacct_on;
return delayacct_on;
#else
return 0;
#endif
return IS_ENABLED(CONFIG_SCHED_INFO);
}
#ifdef CONFIG_SCHEDSTATS

1
kernel/delayacct.c
View file

@ -15,7 +15,6 @@
#include <linux/module.h>
int delayacct_on __read_mostly = 1; /* Delay accounting turned on/off */
EXPORT_SYMBOL_GPL(delayacct_on);
struct kmem_cache *delayacct_cache;
static int __init delayacct_setup_disable(char *str)

37
kernel/sched/stats.h
View file

@ -150,11 +150,6 @@ static inline void psi_sched_switch(struct task_struct *prev,
#endif /* CONFIG_PSI */
#ifdef CONFIG_SCHED_INFO
static inline void sched_info_reset_dequeued(struct task_struct *t)
{
t->sched_info.last_queued = 0;
}
/*
* We are interested in knowing how long it was from the *first* time a
* task was queued to the time that it finally hit a CPU, we call this routine
@ -163,13 +158,12 @@ static inline void sched_info_reset_dequeued(struct task_struct *t)
*/
static inline void sched_info_dequeue(struct rq *rq, struct task_struct *t)
{
unsigned long long now = rq_clock(rq), delta = 0;
unsigned long long delta = 0;
if (sched_info_on()) {
if (t->sched_info.last_queued)
delta = now - t->sched_info.last_queued;
if (t->sched_info.last_queued) {
delta = rq_clock(rq) - t->sched_info.last_queued;
t->sched_info.last_queued = 0;
}
sched_info_reset_dequeued(t);
t->sched_info.run_delay += delta;
rq_sched_info_dequeue(rq, delta);
@ -184,9 +178,10 @@ static void sched_info_arrive(struct rq *rq, struct task_struct *t)
{
unsigned long long now = rq_clock(rq), delta = 0;
if (t->sched_info.last_queued)
if (t->sched_info.last_queued) {
delta = now - t->sched_info.last_queued;
sched_info_reset_dequeued(t);
t->sched_info.last_queued = 0;
}
t->sched_info.run_delay += delta;
t->sched_info.last_arrival = now;
t->sched_info.pcount++;
@ -201,10 +196,8 @@ static void sched_info_arrive(struct rq *rq, struct task_struct *t)
*/
static inline void sched_info_enqueue(struct rq *rq, struct task_struct *t)
{
if (sched_info_on()) {
if (!t->sched_info.last_queued)
t->sched_info.last_queued = rq_clock(rq);
}
if (!t->sched_info.last_queued)
t->sched_info.last_queued = rq_clock(rq);
}
/*
@ -231,7 +224,7 @@ static inline void sched_info_depart(struct rq *rq, struct task_struct *t)
* the idle task.) We are only called when prev != next.
*/
static inline void
__sched_info_switch(struct rq *rq, struct task_struct *prev, struct task_struct *next)
sched_info_switch(struct rq *rq, struct task_struct *prev, struct task_struct *next)
{
/*
* prev now departs the CPU. It's not interesting to record
@ -245,18 +238,8 @@ __sched_info_switch(struct rq *rq, struct task_struct *prev, struct task_struct
sched_info_arrive(rq, next);
}
static inline void
sched_info_switch(struct rq *rq, struct task_struct *prev, struct task_struct *next)
{
if (sched_info_on())
__sched_info_switch(rq, prev, next);
}
#else /* !CONFIG_SCHED_INFO: */
# define sched_info_enqueue(rq, t) do { } while (0)
# define sched_info_reset_dequeued(t) do { } while (0)
# define sched_info_dequeue(rq, t) do { } while (0)
# define sched_info_depart(rq, t) do { } while (0)
# define sched_info_arrive(rq, next) do { } while (0)
# define sched_info_switch(rq, t, next) do { } while (0)
#endif /* CONFIG_SCHED_INFO */