diff options
Diffstat (limited to 'kernel/sched/clock.c')
| -rw-r--r-- | kernel/sched/clock.c | 160 |
1 files changed, 85 insertions, 75 deletions
diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c index e85a725e5c34..a08795e21628 100644 --- a/kernel/sched/clock.c +++ b/kernel/sched/clock.c @@ -58,6 +58,8 @@ #include <linux/percpu.h> #include <linux/ktime.h> #include <linux/sched.h> +#include <linux/nmi.h> +#include <linux/sched/clock.h> #include <linux/static_key.h> #include <linux/workqueue.h> #include <linux/compiler.h> @@ -77,41 +79,88 @@ EXPORT_SYMBOL_GPL(sched_clock); __read_mostly int sched_clock_running; +void sched_clock_init(void) +{ + sched_clock_running = 1; +} + #ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK -static struct static_key __sched_clock_stable = STATIC_KEY_INIT; -static int __sched_clock_stable_early; +/* + * We must start with !__sched_clock_stable because the unstable -> stable + * transition is accurate, while the stable -> unstable transition is not. + * + * Similarly we start with __sched_clock_stable_early, thereby assuming we + * will become stable, such that there's only a single 1 -> 0 transition. + */ +static DEFINE_STATIC_KEY_FALSE(__sched_clock_stable); +static int __sched_clock_stable_early = 1; -int sched_clock_stable(void) +/* + * We want: ktime_get_ns() + gtod_offset == sched_clock() + raw_offset + */ +static __read_mostly u64 raw_offset; +static __read_mostly u64 gtod_offset; + +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 static_key_false(&__sched_clock_stable); + return this_cpu_ptr(&sched_clock_data); } -static void __set_sched_clock_stable(void) +static inline struct sched_clock_data *cpu_sdc(int cpu) { - if (!sched_clock_stable()) - static_key_slow_inc(&__sched_clock_stable); + return &per_cpu(sched_clock_data, cpu); +} - tick_dep_clear(TICK_DEP_BIT_CLOCK_UNSTABLE); +int sched_clock_stable(void) +{ + return static_branch_likely(&__sched_clock_stable); } -void set_sched_clock_stable(void) +static void __set_sched_clock_stable(void) { - __sched_clock_stable_early = 1; + struct sched_clock_data *scd = this_scd(); - smp_mb(); /* matches sched_clock_init() */ + /* + * Attempt to make the (initial) unstable->stable transition continuous. + */ + raw_offset = (scd->tick_gtod + gtod_offset) - (scd->tick_raw); - if (!sched_clock_running) - return; + printk(KERN_INFO "sched_clock: Marking stable (%lld, %lld)->(%lld, %lld)\n", + scd->tick_gtod, gtod_offset, + scd->tick_raw, raw_offset); - __set_sched_clock_stable(); + static_branch_enable(&__sched_clock_stable); + tick_dep_clear(TICK_DEP_BIT_CLOCK_UNSTABLE); } static void __clear_sched_clock_stable(struct work_struct *work) { - /* XXX worry about clock continuity */ - if (sched_clock_stable()) - static_key_slow_dec(&__sched_clock_stable); + struct sched_clock_data *scd = this_scd(); + + /* + * Attempt to make the stable->unstable transition continuous. + * + * Trouble is, this is typically called from the TSC watchdog + * timer, which is late per definition. This means the tick + * values can already be screwy. + * + * Still do what we can. + */ + gtod_offset = (scd->tick_raw + raw_offset) - (scd->tick_gtod); + + printk(KERN_INFO "sched_clock: Marking unstable (%lld, %lld)<-(%lld, %lld)\n", + scd->tick_gtod, gtod_offset, + scd->tick_raw, raw_offset); + static_branch_disable(&__sched_clock_stable); tick_dep_set(TICK_DEP_BIT_CLOCK_UNSTABLE); } @@ -121,47 +170,15 @@ void clear_sched_clock_stable(void) { __sched_clock_stable_early = 0; - smp_mb(); /* matches sched_clock_init() */ - - if (!sched_clock_running) - return; + smp_mb(); /* matches sched_clock_init_late() */ - schedule_work(&sched_clock_work); + if (sched_clock_running == 2) + schedule_work(&sched_clock_work); } -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) +void sched_clock_init_late(void) { - return this_cpu_ptr(&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; - + sched_clock_running = 2; /* * Ensure that it is impossible to not do a static_key update. * @@ -173,8 +190,6 @@ void sched_clock_init(void) if (__sched_clock_stable_early) __set_sched_clock_stable(); - else - __clear_sched_clock_stable(NULL); } /* @@ -216,7 +231,7 @@ again: * scd->tick_gtod + TICK_NSEC); */ - clock = scd->tick_gtod + delta; + clock = scd->tick_gtod + gtod_offset + delta; min_clock = wrap_max(scd->tick_gtod, old_clock); max_clock = wrap_max(old_clock, scd->tick_gtod + TICK_NSEC); @@ -302,7 +317,7 @@ u64 sched_clock_cpu(int cpu) u64 clock; if (sched_clock_stable()) - return sched_clock(); + return sched_clock() + raw_offset; if (unlikely(!sched_clock_running)) return 0ull; @@ -323,23 +338,22 @@ EXPORT_SYMBOL_GPL(sched_clock_cpu); 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()); + /* + * Update these values even if sched_clock_stable(), because it can + * become unstable at any point in time at which point we need some + * values to fall back on. + * + * XXX arguably we can skip this if we expose tsc_clocksource_reliable + */ scd = this_scd(); - now_gtod = ktime_to_ns(ktime_get()); - now = sched_clock(); + scd->tick_raw = sched_clock(); + scd->tick_gtod = ktime_get_ns(); - scd->tick_raw = now; - scd->tick_gtod = now_gtod; - sched_clock_local(scd); + if (!sched_clock_stable() && likely(sched_clock_running)) + sched_clock_local(scd); } /* @@ -366,11 +380,6 @@ 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)) @@ -378,6 +387,7 @@ u64 sched_clock_cpu(int cpu) return sched_clock(); } + #endif /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */ /* |