/* * sched_clock for unstable cpu clocks * * Copyright (C) 2008 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com> * * 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. * sched_clock_cpu(i) -- must be used with local IRQs disabled (implied by NMI) * local_clock() -- is cpu_clock() on the current cpu. * * 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). * * * Notes: * * The !IRQ-safetly of sched_clock() and sched_clock_cpu() comes from things * like cpufreq interrupts that can change the base clock (TSC) multiplier * and cause funny jumps in time -- although the filtering provided by * sched_clock_cpu() should mitigate serious artifacts we cannot rely on it * in general since for !CONFIG_HAVE_UNSTABLE_SCHED_CLOCK we fully rely on * sched_clock(). */#include <linux/spinlock.h>#include <linux/hardirq.h>#include <linux/export.h>#include <linux/percpu.h>#include <linux/ktime.h>#include <linux/sched.h>/* * Scheduler clock - returns current time in nanosec units. * This is default implementation. * Architectures and sub-architectures can override this. */unsigned long long __attribute__((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;#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK__read_mostly int sched_clock_stable;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 &__get_cpu_var(sched_clock_data);}static inline struct sched_clock_data *cpu_sdc(int cpu){ return &per_cpu(sched_clock_data, cpu);}void sched_clock_init(void){ u64 ktime_now = ktime_to_ns(ktime_get()); int cpu; for_each_possible_cpu(cpu) { struct sched_clock_data *scd = cpu_sdc(cpu); scd->tick_raw = 0; scd->tick_gtod = ktime_now; scd->clock = ktime_now; } sched_clock_running = 1;}/* * 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; 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); */ clock = scd->tick_gtod + delta; min_clock = wrap_max(scd->tick_gtod, old_clock); max_clock = wrap_max(old_clock, scd->tick_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; WARN_ON_ONCE(!irqs_disabled()); if (sched_clock_stable) return sched_clock(); if (unlikely(!sched_clock_running)) return 0ull; scd = cpu_sdc(cpu); if (cpu != smp_processor_id()) clock = sched_clock_remote(scd); else clock = sched_clock_local(scd); return clock;}void sched_clock_tick(void){ struct sched_clock_data *scd; u64 now, now_gtod; if (sched_clock_stable) return; if (unlikely(!sched_clock_running)) return; WARN_ON_ONCE(!irqs_disabled()); scd = this_scd(); now_gtod = ktime_to_ns(ktime_get()); now = sched_clock(); scd->tick_raw = now; scd->tick_gtod = now_gtod; 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();}EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);/* * As outlined at the top, provides a fast, high resolution, nanosecond * time source that is monotonic per cpu argument and has bounded drift * between cpus. * * ######################### BIG FAT WARNING ########################## * # when comparing cpu_clock(i) to cpu_clock(j) for i != j, time can # * # go backwards !! # * #################################################################### */u64 cpu_clock(int cpu){ u64 clock; unsigned long flags; local_irq_save(flags); clock = sched_clock_cpu(cpu); local_irq_restore(flags); return clock;}/* * Similar to cpu_clock() for the current cpu. Time will only be observed * to be monotonic if care is taken to only compare timestampt taken on the * same CPU. * * See cpu_clock(). */u64 local_clock(void){ u64 clock; unsigned long flags; local_irq_save(flags); clock = sched_clock_cpu(smp_processor_id()); local_irq_restore(flags); return clock;}#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();}u64 cpu_clock(int cpu){ return sched_clock_cpu(cpu);}u64 local_clock(void){ return sched_clock_cpu(0);}#endif /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */EXPORT_SYMBOL_GPL(cpu_clock);EXPORT_SYMBOL_GPL(local_clock);
/*
* sched_clock for unstable cpu clocks
*
* Copyright (C) 2008 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
*
* 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.
* sched_clock_cpu(i) -- must be used with local IRQs disabled (implied by NMI)
* local_clock() -- is cpu_clock() on the current cpu.
*
* 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).
*
*
* Notes:
*
* The !IRQ-safetly of sched_clock() and sched_clock_cpu() comes from things
* like cpufreq interrupts that can change the base clock (TSC) multiplier
* and cause funny jumps in time -- although the filtering provided by
* sched_clock_cpu() should mitigate serious artifacts we cannot rely on it
* in general since for !CONFIG_HAVE_UNSTABLE_SCHED_CLOCK we fully rely on
* sched_clock().
*/
#include <linux/spinlock.h>
#include <linux/hardirq.h>
#include <linux/export.h>
#include <linux/percpu.h>
#include <linux/ktime.h>
#include <linux/sched.h>
/*
* Scheduler clock - returns current time in nanosec units.
* This is default implementation.
* Architectures and sub-architectures can override this.
*/
unsigned long long __attribute__((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;
#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
__read_mostly int sched_clock_stable;
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 &__get_cpu_var(sched_clock_data);
}
static inline struct sched_clock_data *cpu_sdc(int cpu)
{
return &per_cpu(sched_clock_data, cpu);
}
void sched_clock_init(void)
{
u64 ktime_now = ktime_to_ns(ktime_get());
int cpu;
for_each_possible_cpu(cpu) {
struct sched_clock_data *scd = cpu_sdc(cpu);
scd->tick_raw = 0;
scd->tick_gtod = ktime_now;
scd->clock = ktime_now;
}
sched_clock_running = 1;
}
/*
* 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;
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);
*/
clock = scd->tick_gtod + delta;
min_clock = wrap_max(scd->tick_gtod, old_clock);
max_clock = wrap_max(old_clock, scd->tick_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;
WARN_ON_ONCE(!irqs_disabled());
if (sched_clock_stable)
return sched_clock();
if (unlikely(!sched_clock_running))
return 0ull;
scd = cpu_sdc(cpu);
if (cpu != smp_processor_id())
clock = sched_clock_remote(scd);
else
clock = sched_clock_local(scd);
return clock;
}
void sched_clock_tick(void)
{
struct sched_clock_data *scd;
u64 now, now_gtod;
if (sched_clock_stable)
return;
if (unlikely(!sched_clock_running))
return;
WARN_ON_ONCE(!irqs_disabled());
scd = this_scd();
now_gtod = ktime_to_ns(ktime_get());
now = sched_clock();
scd->tick_raw = now;
scd->tick_gtod = now_gtod;
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();
}
EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);
/*
* As outlined at the top, provides a fast, high resolution, nanosecond
* time source that is monotonic per cpu argument and has bounded drift
* between cpus.
*
* ######################### BIG FAT WARNING ##########################
* # when comparing cpu_clock(i) to cpu_clock(j) for i != j, time can #
* # go backwards !! #
* ####################################################################
*/
u64 cpu_clock(int cpu)
{
u64 clock;
unsigned long flags;
local_irq_save(flags);
clock = sched_clock_cpu(cpu);
local_irq_restore(flags);
return clock;
}
/*
* Similar to cpu_clock() for the current cpu. Time will only be observed
* to be monotonic if care is taken to only compare timestampt taken on the
* same CPU.
*
* See cpu_clock().
*/
u64 local_clock(void)
{
u64 clock;
unsigned long flags;
local_irq_save(flags);
clock = sched_clock_cpu(smp_processor_id());
local_irq_restore(flags);
return clock;
}
#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();
}
u64 cpu_clock(int cpu)
{
return sched_clock_cpu(cpu);
}
u64 local_clock(void)
{
return sched_clock_cpu(0);
}
#endif /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */
EXPORT_SYMBOL_GPL(cpu_clock);
EXPORT_SYMBOL_GPL(local_clock);