Permalink
Switch branches/tags
Nothing to show
Find file Copy path
Fetching contributors…
Cannot retrieve contributors at this time
284 lines (230 sloc) 6.09 KB
/*
* 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>
*
* Create a semi stable clock from a mixture of other events, including:
* - gtod
* - sched_clock()
* - explicit idle events
*
* We use gtod as base and the unstable clock deltas. The deltas are filtered,
* making it monotonic 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).
*
* The clock: sched_clock_cpu() is monotonic per cpu, and should be somewhat
* consistent between cpus (never more than 2 jiffies difference).
*/
#include <linux/spinlock.h>
#include <linux/hardirq.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.
* 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);
}
static __read_mostly int sched_clock_running;
#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
__read_mostly int sched_clock_stable;
struct sched_clock_data {
/*
* Raw spinlock - this is a special case: this might be called
* from within instrumentation code so we dont want to do any
* instrumentation ourselves.
*/
raw_spinlock_t lock;
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->lock = (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED;
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 __update_sched_clock(struct sched_clock_data *scd, u64 now)
{
s64 delta = now - scd->tick_raw;
u64 clock, min_clock, max_clock;
if (unlikely(delta < 0))
delta = 0;
/*
* 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, scd->clock);
max_clock = wrap_max(scd->clock, scd->tick_gtod + TICK_NSEC);
clock = wrap_max(clock, min_clock);
clock = wrap_min(clock, max_clock);
scd->clock = clock;
return scd->clock;
}
static void lock_double_clock(struct sched_clock_data *data1,
struct sched_clock_data *data2)
{
if (data1 < data2) {
__raw_spin_lock(&data1->lock);
__raw_spin_lock(&data2->lock);
} else {
__raw_spin_lock(&data2->lock);
__raw_spin_lock(&data1->lock);
}
}
u64 sched_clock_cpu(int cpu)
{
u64 now, clock, this_clock, remote_clock;
struct sched_clock_data *scd;
if (sched_clock_stable)
return sched_clock();
scd = cpu_sdc(cpu);
/*
* Normally this is not called in NMI context - but if it is,
* trying to do any locking here is totally lethal.
*/
if (unlikely(in_nmi()))
return scd->clock;
if (unlikely(!sched_clock_running))
return 0ull;
WARN_ON_ONCE(!irqs_disabled());
now = sched_clock();
if (cpu != raw_smp_processor_id()) {
struct sched_clock_data *my_scd = this_scd();
lock_double_clock(scd, my_scd);
this_clock = __update_sched_clock(my_scd, now);
remote_clock = scd->clock;
/*
* 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)) {
clock = this_clock;
scd->clock = clock;
} else {
/*
* Should be rare, but possible:
*/
clock = remote_clock;
my_scd->clock = remote_clock;
}
__raw_spin_unlock(&my_scd->lock);
} else {
__raw_spin_lock(&scd->lock);
clock = __update_sched_clock(scd, now);
}
__raw_spin_unlock(&scd->lock);
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();
__raw_spin_lock(&scd->lock);
scd->tick_raw = now;
scd->tick_gtod = now_gtod;
__update_sched_clock(scd, now);
__raw_spin_unlock(&scd->lock);
}
/*
* 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);
#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 /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */
unsigned long long cpu_clock(int cpu)
{
unsigned long long clock;
unsigned long flags;
local_irq_save(flags);
clock = sched_clock_cpu(cpu);
local_irq_restore(flags);
return clock;
}
EXPORT_SYMBOL_GPL(cpu_clock);