Commit c5895d3f authored by Peter Zijlstra's avatar Peter Zijlstra
Browse files

sched: Simplify sched_info_on() 



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: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarThomas Gleixner <tglx@linutronix.de>
Reviewed-by: default avatarIngo Molnar <mingo@kernel.org>
Acked-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
Link: https://lkml.kernel.org/r/20210505111525.121458839@infradead.org
parent 4e29fb70

include/linux/sched/stat.h

+2 −8
Original line number Diff line number Diff line
@@ -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

kernel/delayacct.c

+0 −1
Original line number Diff line number Diff line
@@ -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)

kernel/sched/stats.h

+10 −27
Original line number Diff line number Diff line
@@ -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++;
@@ -201,11 +196,9 @@ 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);

}

}



/*

 * Called when a process ceases being the active-running process involuntarily
@@ -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 */