/* * sched_clock for unstable cpu clocks * * Copyright (C) 2008 Red Hat, Inc., Peter Zijlstra * * Updates and enhancements: * Copyright (C) 2008 Red Hat, Inc. Steven Rostedt <srostedt@redhat.com> * * Based on code by: * Ingo Molnar <mingo@redhat.com> * Guillaume Chazarain <guichaz@gmail.com> * * * What: * * cpu_clock(i) provides a fast (execution time) high resolution * clock with bounded drift between CPUs. The value of cpu_clock(i) * is monotonic for constant i. The timestamp returned is in nanoseconds. * * ######################### BIG FAT WARNING ########################## * # when comparing cpu_clock(i) to cpu_clock(j) for i != j, time can # * # go backwards !! # * #################################################################### * * There is no strict promise about the base, although it tends to start * at 0 on boot (but people really shouldn't rely on that). * * cpu_clock(i) -- can be used from any context, including NMI. * local_clock() -- is cpu_clock() on the current cpu. * * sched_clock_cpu(i) * * How: * * The implementation either uses sched_clock() when * !CONFIG_HAVE_UNSTABLE_SCHED_CLOCK, which means in that case the * sched_clock() is assumed to provide these properties (mostly it means * the architecture provides a globally synchronized highres time source). * * Otherwise it tries to create a semi stable clock from a mixture of other * clocks, including: * * - GTOD (clock monotomic) * - sched_clock() * - explicit idle events * * We use GTOD as base and use sched_clock() deltas to improve resolution. The * deltas are filtered to provide monotonicity and keeping it within an * expected window. * * Furthermore, explicit sleep and wakeup hooks allow us to account for time * that is otherwise invisible (TSC gets stopped). * */#include <linux/spinlock.h>#include <linux/hardirq.h>#include <linux/export.h>#include <linux/percpu.h>#include <linux/ktime.h>#include <linux/sched.h>#include <linux/nmi.h>#include <linux/sched/clock.h>#include <linux/static_key.h>#include <linux/workqueue.h>#include <linux/compiler.h>#include <linux/tick.h> /* * Scheduler clock - returns current time in nanosec units. * This is default implementation. * Architectures and sub-architectures can override this. */unsigned long long __weak sched_clock(void){ return (unsigned long long)(jiffies - INITIAL_JIFFIES) * (NSEC_PER_SEC / HZ);}EXPORT_SYMBOL_GPL(sched_clock); __read_mostly int sched_clock_running; void sched_clock_init(void){ sched_clock_running = 1;} #ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK/* * We must start with !__sched_clock_stable because the unstable -> stable * transition is accurate, while the stable -> unstable transition is not. * * Similarly we start with __sched_clock_stable_early, thereby assuming we * will become stable, such that there's only a single 1 -> 0 transition. */static DEFINE_STATIC_KEY_FALSE(__sched_clock_stable);static int __sched_clock_stable_early = 1; /* * We want: ktime_get_ns() + __gtod_offset == sched_clock() + __sched_clock_offset */__read_mostly u64 __sched_clock_offset;static __read_mostly u64 __gtod_offset; struct sched_clock_data { u64 tick_raw; u64 tick_gtod; u64 clock;}; static DEFINE_PER_CPU_SHARED_ALIGNED(struct sched_clock_data, sched_clock_data); static inline struct sched_clock_data *this_scd(void){ return this_cpu_ptr(&sched_clock_data);} static inline struct sched_clock_data *cpu_sdc(int cpu){ return &per_cpu(sched_clock_data, cpu);} int sched_clock_stable(void){ return static_branch_likely(&__sched_clock_stable);} static void __set_sched_clock_stable(void){ struct sched_clock_data *scd = this_scd(); /* * Attempt to make the (initial) unstable->stable transition continuous. */ __sched_clock_offset = (scd->tick_gtod + __gtod_offset) - (scd->tick_raw); printk(KERN_INFO "sched_clock: Marking stable (%lld, %lld)->(%lld, %lld)\n", scd->tick_gtod, __gtod_offset, scd->tick_raw, __sched_clock_offset); static_branch_enable(&__sched_clock_stable); tick_dep_clear(TICK_DEP_BIT_CLOCK_UNSTABLE);} static void __sched_clock_work(struct work_struct *work){ static_branch_disable(&__sched_clock_stable);} static DECLARE_WORK(sched_clock_work, __sched_clock_work); static void __clear_sched_clock_stable(void){ struct sched_clock_data *scd = this_scd(); /* * Attempt to make the stable->unstable transition continuous. * * Trouble is, this is typically called from the TSC watchdog * timer, which is late per definition. This means the tick * values can already be screwy. * * Still do what we can. */ __gtod_offset = (scd->tick_raw + __sched_clock_offset) - (scd->tick_gtod); printk(KERN_INFO "sched_clock: Marking unstable (%lld, %lld)<-(%lld, %lld)\n", scd->tick_gtod, __gtod_offset, scd->tick_raw, __sched_clock_offset); tick_dep_set(TICK_DEP_BIT_CLOCK_UNSTABLE); if (sched_clock_stable()) schedule_work(&sched_clock_work);} void clear_sched_clock_stable(void){ __sched_clock_stable_early = 0; smp_mb(); /* matches sched_clock_init_late() */ if (sched_clock_running == 2) __clear_sched_clock_stable();} void sched_clock_init_late(void){ sched_clock_running = 2; /* * Ensure that it is impossible to not do a static_key update. * * Either {set,clear}_sched_clock_stable() must see sched_clock_running * and do the update, or we must see their __sched_clock_stable_early * and do the update, or both. */ smp_mb(); /* matches {set,clear}_sched_clock_stable() */ if (__sched_clock_stable_early) __set_sched_clock_stable();} /* * min, max except they take wrapping into account */ static inline u64 wrap_min(u64 x, u64 y){ return (s64)(x - y) < 0 ? x : y;} static inline u64 wrap_max(u64 x, u64 y){ return (s64)(x - y) > 0 ? x : y;} /* * update the percpu scd from the raw @now value * * - filter out backward motion * - use the GTOD tick value to create a window to filter crazy TSC values */static u64 sched_clock_local(struct sched_clock_data *scd){ u64 now, clock, old_clock, min_clock, max_clock, gtod; s64 delta; again: now = sched_clock(); delta = now - scd->tick_raw; if (unlikely(delta < 0)) delta = 0; old_clock = scd->clock; /* * scd->clock = clamp(scd->tick_gtod + delta, * max(scd->tick_gtod, scd->clock), * scd->tick_gtod + TICK_NSEC); */ gtod = scd->tick_gtod + __gtod_offset; clock = gtod + delta; min_clock = wrap_max(gtod, old_clock); max_clock = wrap_max(old_clock, gtod + TICK_NSEC); clock = wrap_max(clock, min_clock); clock = wrap_min(clock, max_clock); if (cmpxchg64(&scd->clock, old_clock, clock) != old_clock) goto again; return clock;} static u64 sched_clock_remote(struct sched_clock_data *scd){ struct sched_clock_data *my_scd = this_scd(); u64 this_clock, remote_clock; u64 *ptr, old_val, val; #if BITS_PER_LONG != 64again: /* * Careful here: The local and the remote clock values need to * be read out atomic as we need to compare the values and * then update either the local or the remote side. So the * cmpxchg64 below only protects one readout. * * We must reread via sched_clock_local() in the retry case on * 32bit as an NMI could use sched_clock_local() via the * tracer and hit between the readout of * the low32bit and the high 32bit portion. */ this_clock = sched_clock_local(my_scd); /* * We must enforce atomic readout on 32bit, otherwise the * update on the remote cpu can hit inbetween the readout of * the low32bit and the high 32bit portion. */ remote_clock = cmpxchg64(&scd->clock, 0, 0);#else /* * On 64bit the read of [my]scd->clock is atomic versus the * update, so we can avoid the above 32bit dance. */ sched_clock_local(my_scd);again: this_clock = my_scd->clock; remote_clock = scd->clock;#endif /* * Use the opportunity that we have both locks * taken to couple the two clocks: we take the * larger time as the latest time for both * runqueues. (this creates monotonic movement) */ if (likely((s64)(remote_clock - this_clock) < 0)) { ptr = &scd->clock; old_val = remote_clock; val = this_clock; } else { /* * Should be rare, but possible: */ ptr = &my_scd->clock; old_val = this_clock; val = remote_clock; } if (cmpxchg64(ptr, old_val, val) != old_val) goto again; return val;} /* * Similar to cpu_clock(), but requires local IRQs to be disabled. * * See cpu_clock(). */u64 sched_clock_cpu(int cpu){ struct sched_clock_data *scd; u64 clock; if (sched_clock_stable()) return sched_clock() + __sched_clock_offset; if (unlikely(!sched_clock_running)) return 0ull; preempt_disable_notrace(); scd = cpu_sdc(cpu); if (cpu != smp_processor_id()) clock = sched_clock_remote(scd); else clock = sched_clock_local(scd); preempt_enable_notrace(); return clock;}EXPORT_SYMBOL_GPL(sched_clock_cpu); void sched_clock_tick(void){ struct sched_clock_data *scd; WARN_ON_ONCE(!irqs_disabled()); /* * Update these values even if sched_clock_stable(), because it can * become unstable at any point in time at which point we need some * values to fall back on. * * XXX arguably we can skip this if we expose tsc_clocksource_reliable */ scd = this_scd(); scd->tick_raw = sched_clock(); scd->tick_gtod = ktime_get_ns(); if (!sched_clock_stable() && likely(sched_clock_running)) sched_clock_local(scd);} /* * We are going deep-idle (irqs are disabled): */void sched_clock_idle_sleep_event(void){ sched_clock_cpu(smp_processor_id());}EXPORT_SYMBOL_GPL(sched_clock_idle_sleep_event); /* * We just idled delta nanoseconds (called with irqs disabled): */void sched_clock_idle_wakeup_event(u64 delta_ns){ if (timekeeping_suspended) return; sched_clock_tick(); touch_softlockup_watchdog_sched();}EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event); #else /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */ u64 sched_clock_cpu(int cpu){ if (unlikely(!sched_clock_running)) return 0; return sched_clock();} #endif /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */ /* * Running clock - returns the time that has elapsed while a guest has been * running. * On a guest this value should be local_clock minus the time the guest was * suspended by the hypervisor (for any reason). * On bare metal this function should return the same as local_clock. * Architectures and sub-architectures can override this. */u64 __weak running_clock(void){ return local_clock();}
/*
* sched_clock for unstable cpu clocks
*
* Copyright (C) 2008 Red Hat, Inc., Peter Zijlstra
*
* Updates and enhancements:
* Copyright (C) 2008 Red Hat, Inc. Steven Rostedt <srostedt@redhat.com>
*
* Based on code by:
* Ingo Molnar <mingo@redhat.com>
* Guillaume Chazarain <guichaz@gmail.com>
*
*
* What:
*
* cpu_clock(i) provides a fast (execution time) high resolution
* clock with bounded drift between CPUs. The value of cpu_clock(i)
* is monotonic for constant i. The timestamp returned is in nanoseconds.
*
* ######################### BIG FAT WARNING ##########################
* # when comparing cpu_clock(i) to cpu_clock(j) for i != j, time can #
* # go backwards !! #
* ####################################################################
*
* There is no strict promise about the base, although it tends to start
* at 0 on boot (but people really shouldn't rely on that).
*
* cpu_clock(i) -- can be used from any context, including NMI.
* local_clock() -- is cpu_clock() on the current cpu.
*
* sched_clock_cpu(i)
*
* How:
*
* The implementation either uses sched_clock() when
* !CONFIG_HAVE_UNSTABLE_SCHED_CLOCK, which means in that case the
* sched_clock() is assumed to provide these properties (mostly it means
* the architecture provides a globally synchronized highres time source).
*
* Otherwise it tries to create a semi stable clock from a mixture of other
* clocks, including:
*
* - GTOD (clock monotomic)
* - sched_clock()
* - explicit idle events
*
* We use GTOD as base and use sched_clock() deltas to improve resolution. The
* deltas are filtered to provide monotonicity and keeping it within an
* expected window.
*
* Furthermore, explicit sleep and wakeup hooks allow us to account for time
* that is otherwise invisible (TSC gets stopped).
*
*/
#include <linux/spinlock.h>
#include <linux/hardirq.h>
#include <linux/export.h>
#include <linux/percpu.h>
#include <linux/ktime.h>
#include <linux/sched.h>
#include <linux/nmi.h>
#include <linux/sched/clock.h>
#include <linux/static_key.h>
#include <linux/workqueue.h>
#include <linux/compiler.h>
#include <linux/tick.h>
/*
* Scheduler clock - returns current time in nanosec units.
* This is default implementation.
* Architectures and sub-architectures can override this.
*/
unsigned long long __weak sched_clock(void)
{
return (unsigned long long)(jiffies - INITIAL_JIFFIES)
* (NSEC_PER_SEC / HZ);
}
EXPORT_SYMBOL_GPL(sched_clock);
__read_mostly int sched_clock_running;
void sched_clock_init(void)
{
sched_clock_running = 1;
}
#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
/*
* We must start with !__sched_clock_stable because the unstable -> stable
* transition is accurate, while the stable -> unstable transition is not.
*
* Similarly we start with __sched_clock_stable_early, thereby assuming we
* will become stable, such that there's only a single 1 -> 0 transition.
*/
static DEFINE_STATIC_KEY_FALSE(__sched_clock_stable);
static int __sched_clock_stable_early = 1;
/*
* We want: ktime_get_ns() + __gtod_offset == sched_clock() + __sched_clock_offset
*/
__read_mostly u64 __sched_clock_offset;
static __read_mostly u64 __gtod_offset;
struct sched_clock_data {
u64 tick_raw;
u64 tick_gtod;
u64 clock;
};
static DEFINE_PER_CPU_SHARED_ALIGNED(struct sched_clock_data, sched_clock_data);
static inline struct sched_clock_data *this_scd(void)
{
return this_cpu_ptr(&sched_clock_data);
}
static inline struct sched_clock_data *cpu_sdc(int cpu)
{
return &per_cpu(sched_clock_data, cpu);
}
int sched_clock_stable(void)
{
return static_branch_likely(&__sched_clock_stable);
}
static void __set_sched_clock_stable(void)
{
struct sched_clock_data *scd = this_scd();
/*
* Attempt to make the (initial) unstable->stable transition continuous.
*/
__sched_clock_offset = (scd->tick_gtod + __gtod_offset) - (scd->tick_raw);
printk(KERN_INFO "sched_clock: Marking stable (%lld, %lld)->(%lld, %lld)\n",
scd->tick_gtod, __gtod_offset,
scd->tick_raw, __sched_clock_offset);
static_branch_enable(&__sched_clock_stable);
tick_dep_clear(TICK_DEP_BIT_CLOCK_UNSTABLE);
}
static void __sched_clock_work(struct work_struct *work)
{
static_branch_disable(&__sched_clock_stable);
}
static DECLARE_WORK(sched_clock_work, __sched_clock_work);
static void __clear_sched_clock_stable(void)
{
struct sched_clock_data *scd = this_scd();
/*
* Attempt to make the stable->unstable transition continuous.
*
* Trouble is, this is typically called from the TSC watchdog
* timer, which is late per definition. This means the tick
* values can already be screwy.
*
* Still do what we can.
*/
__gtod_offset = (scd->tick_raw + __sched_clock_offset) - (scd->tick_gtod);
printk(KERN_INFO "sched_clock: Marking unstable (%lld, %lld)<-(%lld, %lld)\n",
scd->tick_gtod, __gtod_offset,
scd->tick_raw, __sched_clock_offset);
tick_dep_set(TICK_DEP_BIT_CLOCK_UNSTABLE);
if (sched_clock_stable())
schedule_work(&sched_clock_work);
}
void clear_sched_clock_stable(void)
{
__sched_clock_stable_early = 0;
smp_mb(); /* matches sched_clock_init_late() */
if (sched_clock_running == 2)
__clear_sched_clock_stable();
}
void sched_clock_init_late(void)
{
sched_clock_running = 2;
/*
* Ensure that it is impossible to not do a static_key update.
*
* Either {set,clear}_sched_clock_stable() must see sched_clock_running
* and do the update, or we must see their __sched_clock_stable_early
* and do the update, or both.
*/
smp_mb(); /* matches {set,clear}_sched_clock_stable() */
if (__sched_clock_stable_early)
__set_sched_clock_stable();
}
/*
* min, max except they take wrapping into account
*/
static inline u64 wrap_min(u64 x, u64 y)
{
return (s64)(x - y) < 0 ? x : y;
}
static inline u64 wrap_max(u64 x, u64 y)
{
return (s64)(x - y) > 0 ? x : y;
}
/*
* update the percpu scd from the raw @now value
*
* - filter out backward motion
* - use the GTOD tick value to create a window to filter crazy TSC values
*/
static u64 sched_clock_local(struct sched_clock_data *scd)
{
u64 now, clock, old_clock, min_clock, max_clock, gtod;
s64 delta;
again:
now = sched_clock();
delta = now - scd->tick_raw;
if (unlikely(delta < 0))
delta = 0;
old_clock = scd->clock;
/*
* scd->clock = clamp(scd->tick_gtod + delta,
* max(scd->tick_gtod, scd->clock),
* scd->tick_gtod + TICK_NSEC);
*/
gtod = scd->tick_gtod + __gtod_offset;
clock = gtod + delta;
min_clock = wrap_max(gtod, old_clock);
max_clock = wrap_max(old_clock, gtod + TICK_NSEC);
clock = wrap_max(clock, min_clock);
clock = wrap_min(clock, max_clock);
if (cmpxchg64(&scd->clock, old_clock, clock) != old_clock)
goto again;
return clock;
}
static u64 sched_clock_remote(struct sched_clock_data *scd)
{
struct sched_clock_data *my_scd = this_scd();
u64 this_clock, remote_clock;
u64 *ptr, old_val, val;
#if BITS_PER_LONG != 64
again:
/*
* Careful here: The local and the remote clock values need to
* be read out atomic as we need to compare the values and
* then update either the local or the remote side. So the
* cmpxchg64 below only protects one readout.
*
* We must reread via sched_clock_local() in the retry case on
* 32bit as an NMI could use sched_clock_local() via the
* tracer and hit between the readout of
* the low32bit and the high 32bit portion.
*/
this_clock = sched_clock_local(my_scd);
/*
* We must enforce atomic readout on 32bit, otherwise the
* update on the remote cpu can hit inbetween the readout of
* the low32bit and the high 32bit portion.
*/
remote_clock = cmpxchg64(&scd->clock, 0, 0);
#else
/*
* On 64bit the read of [my]scd->clock is atomic versus the
* update, so we can avoid the above 32bit dance.
*/
sched_clock_local(my_scd);
again:
this_clock = my_scd->clock;
remote_clock = scd->clock;
#endif
/*
* Use the opportunity that we have both locks
* taken to couple the two clocks: we take the
* larger time as the latest time for both
* runqueues. (this creates monotonic movement)
*/
if (likely((s64)(remote_clock - this_clock) < 0)) {
ptr = &scd->clock;
old_val = remote_clock;
val = this_clock;
} else {
/*
* Should be rare, but possible:
*/
ptr = &my_scd->clock;
old_val = this_clock;
val = remote_clock;
}
if (cmpxchg64(ptr, old_val, val) != old_val)
goto again;
return val;
}
/*
* Similar to cpu_clock(), but requires local IRQs to be disabled.
*
* See cpu_clock().
*/
u64 sched_clock_cpu(int cpu)
{
struct sched_clock_data *scd;
u64 clock;
if (sched_clock_stable())
return sched_clock() + __sched_clock_offset;
if (unlikely(!sched_clock_running))
return 0ull;
preempt_disable_notrace();
scd = cpu_sdc(cpu);
if (cpu != smp_processor_id())
clock = sched_clock_remote(scd);
else
clock = sched_clock_local(scd);
preempt_enable_notrace();
return clock;
}
EXPORT_SYMBOL_GPL(sched_clock_cpu);
void sched_clock_tick(void)
{
struct sched_clock_data *scd;
WARN_ON_ONCE(!irqs_disabled());
/*
* Update these values even if sched_clock_stable(), because it can
* become unstable at any point in time at which point we need some
* values to fall back on.
*
* XXX arguably we can skip this if we expose tsc_clocksource_reliable
*/
scd = this_scd();
scd->tick_raw = sched_clock();
scd->tick_gtod = ktime_get_ns();
if (!sched_clock_stable() && likely(sched_clock_running))
sched_clock_local(scd);
}
/*
* We are going deep-idle (irqs are disabled):
*/
void sched_clock_idle_sleep_event(void)
{
sched_clock_cpu(smp_processor_id());
}
EXPORT_SYMBOL_GPL(sched_clock_idle_sleep_event);
/*
* We just idled delta nanoseconds (called with irqs disabled):
*/
void sched_clock_idle_wakeup_event(u64 delta_ns)
{
if (timekeeping_suspended)
return;
sched_clock_tick();
touch_softlockup_watchdog_sched();
}
EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);
#else /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */
u64 sched_clock_cpu(int cpu)
{
if (unlikely(!sched_clock_running))
return 0;
return sched_clock();
}
#endif /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */
/*
* Running clock - returns the time that has elapsed while a guest has been
* running.
* On a guest this value should be local_clock minus the time the guest was
* suspended by the hypervisor (for any reason).
* On bare metal this function should return the same as local_clock.
* Architectures and sub-architectures can override this.
*/
u64 __weak running_clock(void)
{
return local_clock();
}