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Commit b342501c authored by Ingo Molnar's avatar Ingo Molnar
Browse files

sched: allow architectures to specify sched_clock_stable 



Allow CONFIG_HAVE_UNSTABLE_SCHED_CLOCK architectures to still specify
that their sched_clock() implementation is reliable.

This will be used by x86 to switch on a faster sched_clock_cpu()
implementation on certain CPU types.

Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 694593e3

include/linux/sched.h

+10 −0
Original line number Diff line number Diff line
@@ -1670,6 +1670,16 @@ static inline int set_cpus_allowed(struct task_struct *p, cpumask_t new_mask) 
	return set_cpus_allowed_ptr(p, &new_mask);

}



/*

 * Architectures can set this to 1 if they have specified

 * CONFIG_HAVE_UNSTABLE_SCHED_CLOCK in their arch Kconfig,

 * but then during bootup it turns out that sched_clock()

 * is reliable after all:

 */

#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK

extern int sched_clock_stable;

#endif



extern unsigned long long sched_clock(void);



extern void sched_clock_init(void);

kernel/sched_clock.c

+20 −25
Original line number Diff line number Diff line
@@ -24,11 +24,11 @@ 
 * The clock: sched_clock_cpu() is monotonic per cpu, and should be somewhat

 * consistent between cpus (never more than 2 jiffies difference).

 */

#include <linux/sched.h>

#include <linux/percpu.h>

#include <linux/spinlock.h>

#include <linux/ktime.h>

#include <linux/module.h>

#include <linux/percpu.h>

#include <linux/ktime.h>

#include <linux/sched.h>



/*

 * Scheduler clock - returns current time in nanosec units.
@@ -43,6 +43,10 @@ unsigned long long __attribute__((weak)) sched_clock(void) 
static __read_mostly int sched_clock_running;



#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK

__read_mostly int sched_clock_stable;

#else

static const int sched_clock_stable = 1;

#endif



struct sched_clock_data {

	/*
@@ -116,6 +120,9 @@ static u64 __update_sched_clock(struct sched_clock_data *scd, u64 now) 
	if (unlikely(delta < 0))

		delta = 0;



	if (unlikely(!sched_clock_running))

		return 0ull;



	/*

	 * scd->clock = clamp(scd->tick_gtod + delta,

	 *		      max(scd->tick_gtod, scd->clock),
@@ -148,12 +155,13 @@ static void lock_double_clock(struct sched_clock_data *data1, 


u64 sched_clock_cpu(int cpu)

{

	struct sched_clock_data *scd = cpu_sdc(cpu);

	u64 now, clock, this_clock, remote_clock;

	struct sched_clock_data *scd;



	if (unlikely(!sched_clock_running))

		return 0ull;

	if (sched_clock_stable)

		return sched_clock();



	scd = cpu_sdc(cpu);

	WARN_ON_ONCE(!irqs_disabled());

	now = sched_clock();
@@ -193,6 +201,8 @@ u64 sched_clock_cpu(int cpu) 
	return clock;

}



#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK



void sched_clock_tick(void)

{

	struct sched_clock_data *scd = this_scd();
@@ -235,22 +245,7 @@ void sched_clock_idle_wakeup_event(u64 delta_ns) 
}

EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);



#else /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */



void sched_clock_init(void)

{

	sched_clock_running = 1;

}



u64 sched_clock_cpu(int cpu)

{

	if (unlikely(!sched_clock_running))

		return 0;



	return sched_clock();

}



#endif

#endif /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */



unsigned long long cpu_clock(int cpu)

{