mirror of
https://github.com/edk2-porting/linux-next.git
synced 2024-12-25 13:43:55 +08:00
c676329abb
For people who otherwise get to write: cpu_clock(smp_processor_id()), there is now: local_clock(). Also, as per suggestion from Andrew, provide some documentation on the various clock interfaces, and minimize the unsigned long long vs u64 mess. Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Jens Axboe <jaxboe@fusionio.com> LKML-Reference: <1275052414.1645.52.camel@laptop> Signed-off-by: Ingo Molnar <mingo@elte.hu>
351 lines
8.0 KiB
C
351 lines
8.0 KiB
C
/*
|
|
* 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/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);
|
|
}
|
|
EXPORT_SYMBOL_GPL(sched_clock);
|
|
|
|
static __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;
|
|
|
|
sched_clock_local(my_scd);
|
|
again:
|
|
this_clock = my_scd->clock;
|
|
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)) {
|
|
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);
|