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author | Peter Zijlstra <a.p.zijlstra@chello.nl> | 2008-05-03 18:29:28 +0200 |
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committer | Ingo Molnar <mingo@elte.hu> | 2008-05-05 23:56:18 +0200 |
commit | 3e51f33fcc7f55e6df25d15b55ed10c8b4da84cd (patch) | |
tree | 3752f9ea8e014ec40e95a1b197b0a3d18e1056a8 /kernel/sched_clock.c | |
parent | sched, x86: add HAVE_UNSTABLE_SCHED_CLOCK (diff) | |
download | linux-3e51f33fcc7f55e6df25d15b55ed10c8b4da84cd.tar.xz linux-3e51f33fcc7f55e6df25d15b55ed10c8b4da84cd.zip |
sched: add optional support for CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
this replaces the rq->clock stuff (and possibly cpu_clock()).
- architectures that have an 'imperfect' hardware clock can set
CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
- the 'jiffie' window might be superfulous when we update tick_gtod
before the __update_sched_clock() call in sched_clock_tick()
- cpu_clock() might be implemented as:
sched_clock_cpu(smp_processor_id())
if the accuracy proves good enough - how far can TSC drift in a
single jiffie when considering the filtering and idle hooks?
[ mingo@elte.hu: various fixes and cleanups ]
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/sched_clock.c')
-rw-r--r-- | kernel/sched_clock.c | 236 |
1 files changed, 236 insertions, 0 deletions
diff --git a/kernel/sched_clock.c b/kernel/sched_clock.c new file mode 100644 index 000000000000..9c597e37f7de --- /dev/null +++ b/kernel/sched_clock.c @@ -0,0 +1,236 @@ +/* + * sched_clock for unstable cpu clocks + * + * Copyright (C) 2008 Red Hat, Inc., Peter Zijlstra <pzijlstr@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 + * - jiffies + * - 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. This window + * is set up using jiffies. + * + * 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 1 jiffies difference). + */ +#include <linux/sched.h> +#include <linux/percpu.h> +#include <linux/spinlock.h> +#include <linux/ktime.h> +#include <linux/module.h> + + +#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK + +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; + + unsigned long prev_jiffies; + u64 prev_raw; + 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()); + u64 now = 0; + 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->prev_jiffies = jiffies; + scd->prev_raw = now; + scd->tick_raw = now; + scd->tick_gtod = ktime_now; + scd->clock = ktime_now; + } +} + +/* + * update the percpu scd from the raw @now value + * + * - filter out backward motion + * - use jiffies to generate a min,max window to clip the raw values + */ +static void __update_sched_clock(struct sched_clock_data *scd, u64 now) +{ + unsigned long now_jiffies = jiffies; + long delta_jiffies = now_jiffies - scd->prev_jiffies; + u64 clock = scd->clock; + u64 min_clock, max_clock; + s64 delta = now - scd->prev_raw; + + WARN_ON_ONCE(!irqs_disabled()); + min_clock = scd->tick_gtod + delta_jiffies * TICK_NSEC; + + if (unlikely(delta < 0)) { + clock++; + goto out; + } + + max_clock = min_clock + TICK_NSEC; + + if (unlikely(clock + delta > max_clock)) { + if (clock < max_clock) + clock = max_clock; + else + clock++; + } else { + clock += delta; + } + + out: + if (unlikely(clock < min_clock)) + clock = min_clock; + + scd->prev_raw = now; + scd->prev_jiffies = now_jiffies; + scd->clock = 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) +{ + struct sched_clock_data *scd = cpu_sdc(cpu); + u64 now, clock; + + WARN_ON_ONCE(!irqs_disabled()); + now = sched_clock(); + + if (cpu != raw_smp_processor_id()) { + /* + * in order to update a remote cpu's clock based on our + * unstable raw time rebase it against: + * tick_raw (offset between raw counters) + * tick_gotd (tick offset between cpus) + */ + struct sched_clock_data *my_scd = this_scd(); + + lock_double_clock(scd, my_scd); + + now -= my_scd->tick_raw; + now += scd->tick_raw; + + now -= my_scd->tick_gtod; + now += scd->tick_gtod; + + __raw_spin_unlock(&my_scd->lock); + } else { + __raw_spin_lock(&scd->lock); + } + + __update_sched_clock(scd, now); + clock = scd->clock; + + __raw_spin_unlock(&scd->lock); + + return clock; +} + +void sched_clock_tick(void) +{ + struct sched_clock_data *scd = this_scd(); + u64 now, now_gtod; + + WARN_ON_ONCE(!irqs_disabled()); + + now = sched_clock(); + now_gtod = ktime_to_ns(ktime_get()); + + __raw_spin_lock(&scd->lock); + __update_sched_clock(scd, now); + /* + * update tick_gtod after __update_sched_clock() because that will + * already observe 1 new jiffy; adding a new tick_gtod to that would + * increase the clock 2 jiffies. + */ + scd->tick_raw = now; + scd->tick_gtod = now_gtod; + __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) +{ + struct sched_clock_data *scd = this_scd(); + u64 now = sched_clock(); + + /* + * Override the previous timestamp and ignore all + * sched_clock() deltas that occured while we idled, + * and use the PM-provided delta_ns to advance the + * rq clock: + */ + __raw_spin_lock(&scd->lock); + scd->prev_raw = now; + scd->clock += delta_ns; + __raw_spin_unlock(&scd->lock); + + touch_softlockup_watchdog(); +} +EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event); + +#endif + +/* + * 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 * (NSEC_PER_SEC / HZ); +} |