diff options
Diffstat (limited to 'kernel/sched_clock.c')
-rw-r--r-- | kernel/sched_clock.c | 224 |
1 files changed, 71 insertions, 153 deletions
diff --git a/kernel/sched_clock.c b/kernel/sched_clock.c index 22ed55d1167..e8ab096ddfe 100644 --- a/kernel/sched_clock.c +++ b/kernel/sched_clock.c @@ -12,19 +12,17 @@ * * 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. + * 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 1 jiffies difference). + * consistent between cpus (never more than 2 jiffies difference). */ #include <linux/sched.h> #include <linux/percpu.h> @@ -32,13 +30,19 @@ #include <linux/ktime.h> #include <linux/module.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 * (NSEC_PER_SEC / HZ); +} -#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK +static __read_mostly int sched_clock_running; -#define MULTI_SHIFT 15 -/* Max is double, Min is 1/2 */ -#define MAX_MULTI (2LL << MULTI_SHIFT) -#define MIN_MULTI (1LL << (MULTI_SHIFT-1)) +#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK struct sched_clock_data { /* @@ -48,15 +52,9 @@ struct sched_clock_data { */ raw_spinlock_t lock; - unsigned long tick_jiffies; - u64 prev_raw; u64 tick_raw; u64 tick_gtod; u64 clock; - s64 multi; -#ifdef CONFIG_NO_HZ - int check_max; -#endif }; static DEFINE_PER_CPU_SHARED_ALIGNED(struct sched_clock_data, sched_clock_data); @@ -71,121 +69,69 @@ static inline struct sched_clock_data *cpu_sdc(int cpu) return &per_cpu(sched_clock_data, cpu); } -static __read_mostly int sched_clock_running; - void sched_clock_init(void) { u64 ktime_now = ktime_to_ns(ktime_get()); - unsigned long now_jiffies = jiffies; 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_jiffies = now_jiffies; - scd->prev_raw = 0; scd->tick_raw = 0; scd->tick_gtod = ktime_now; scd->clock = ktime_now; - scd->multi = 1 << MULTI_SHIFT; -#ifdef CONFIG_NO_HZ - scd->check_max = 1; -#endif } sched_clock_running = 1; } -#ifdef CONFIG_NO_HZ /* - * The dynamic ticks makes the delta jiffies inaccurate. This - * prevents us from checking the maximum time update. - * Disable the maximum check during stopped ticks. + * min,max except they take wrapping into account */ -void sched_clock_tick_stop(int cpu) -{ - struct sched_clock_data *scd = cpu_sdc(cpu); - - scd->check_max = 0; -} -void sched_clock_tick_start(int cpu) +static inline u64 wrap_min(u64 x, u64 y) { - struct sched_clock_data *scd = cpu_sdc(cpu); - - scd->check_max = 1; + return (s64)(x - y) < 0 ? x : y; } -static int check_max(struct sched_clock_data *scd) +static inline u64 wrap_max(u64 x, u64 y) { - return scd->check_max; + return (s64)(x - y) > 0 ? x : y; } -#else -static int check_max(struct sched_clock_data *scd) -{ - return 1; -} -#endif /* CONFIG_NO_HZ */ /* * 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 + * - use the GTOD tick value to create a window to filter crazy TSC values */ -static void __update_sched_clock(struct sched_clock_data *scd, u64 now, u64 *time) +static u64 __update_sched_clock(struct sched_clock_data *scd, u64 now) { - unsigned long now_jiffies = jiffies; - long delta_jiffies = now_jiffies - scd->tick_jiffies; - u64 clock = scd->clock; - u64 min_clock, max_clock; - s64 delta = now - scd->prev_raw; + s64 delta = now - scd->tick_raw; + u64 clock, min_clock, max_clock; WARN_ON_ONCE(!irqs_disabled()); - /* - * At schedule tick the clock can be just under the gtod. We don't - * want to push it too prematurely. - */ - min_clock = scd->tick_gtod + (delta_jiffies * TICK_NSEC); - if (min_clock > TICK_NSEC) - min_clock -= TICK_NSEC / 2; - - if (unlikely(delta < 0)) { - clock++; - goto out; - } + if (unlikely(delta < 0)) + delta = 0; /* - * The clock must stay within a jiffie of the gtod. - * But since we may be at the start of a jiffy or the end of one - * we add another jiffy buffer. + * scd->clock = clamp(scd->tick_gtod + delta, + * max(scd->tick_gtod, scd->clock), + * scd->tick_gtod + TICK_NSEC); */ - max_clock = scd->tick_gtod + (2 + delta_jiffies) * TICK_NSEC; - delta *= scd->multi; - delta >>= MULTI_SHIFT; + clock = scd->tick_gtod + delta; + min_clock = wrap_max(scd->tick_gtod, scd->clock); + max_clock = scd->tick_gtod + TICK_NSEC; - if (unlikely(clock + delta > max_clock) && check_max(scd)) { - if (clock < max_clock) - clock = max_clock; - else - clock++; - } else { - clock += delta; - } + clock = wrap_max(clock, min_clock); + clock = wrap_min(clock, max_clock); - out: - if (unlikely(clock < min_clock)) - clock = min_clock; + scd->clock = clock; - if (time) - *time = clock; - else { - scd->prev_raw = now; - scd->clock = clock; - } + return scd->clock; } static void lock_double_clock(struct sched_clock_data *data1, @@ -203,7 +149,7 @@ static void lock_double_clock(struct sched_clock_data *data1, u64 sched_clock_cpu(int cpu) { struct sched_clock_data *scd = cpu_sdc(cpu); - u64 now, clock; + u64 now, clock, this_clock, remote_clock; if (unlikely(!sched_clock_running)) return 0ull; @@ -212,43 +158,44 @@ u64 sched_clock_cpu(int cpu) 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; + this_clock = __update_sched_clock(my_scd, now); + remote_clock = scd->clock; - now += my_scd->tick_gtod; - now -= scd->tick_gtod; + /* + * 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); - - __update_sched_clock(scd, now, &clock); - - __raw_spin_unlock(&scd->lock); - } else { __raw_spin_lock(&scd->lock); - __update_sched_clock(scd, now, NULL); - clock = scd->clock; - __raw_spin_unlock(&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 = this_scd(); - unsigned long now_jiffies = jiffies; - s64 mult, delta_gtod, delta_raw; u64 now, now_gtod; if (unlikely(!sched_clock_running)) @@ -260,29 +207,9 @@ void sched_clock_tick(void) now = sched_clock(); __raw_spin_lock(&scd->lock); - __update_sched_clock(scd, now, NULL); - /* - * 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. - */ - delta_gtod = now_gtod - scd->tick_gtod; - delta_raw = now - scd->tick_raw; - - if ((long)delta_raw > 0) { - mult = delta_gtod << MULTI_SHIFT; - do_div(mult, delta_raw); - scd->multi = mult; - if (scd->multi > MAX_MULTI) - scd->multi = MAX_MULTI; - else if (scd->multi < MIN_MULTI) - scd->multi = MIN_MULTI; - } else - scd->multi = 1 << MULTI_SHIFT; - scd->tick_raw = now; scd->tick_gtod = now_gtod; - scd->tick_jiffies = now_jiffies; + __update_sched_clock(scd, now); __raw_spin_unlock(&scd->lock); } @@ -300,37 +227,28 @@ EXPORT_SYMBOL_GPL(sched_clock_idle_sleep_event); */ 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; - scd->multi = 1 << MULTI_SHIFT; - __raw_spin_unlock(&scd->lock); - + sched_clock_tick(); touch_softlockup_watchdog(); } EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event); -#endif +#else /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */ -/* - * 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) +void sched_clock_init(void) { - return (unsigned long long)jiffies * (NSEC_PER_SEC / HZ); + sched_clock_running = 1; } +u64 sched_clock_cpu(int cpu) +{ + if (unlikely(!sched_clock_running)) + return 0; + + return sched_clock(); +} + +#endif + unsigned long long cpu_clock(int cpu) { unsigned long long clock; |