__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);
}
{
__sched_clock_stable_early = 0;
- smp_mb(); /* matches sched_clock_init() */
-
- if (!sched_clock_running)
- return;
-
- 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)
-{
- return this_cpu_ptr(&sched_clock_data);
-}
+ smp_mb(); /* matches sched_clock_init_late() */
-static inline struct sched_clock_data *cpu_sdc(int cpu)
-{
- return &per_cpu(sched_clock_data, cpu);
+ if (sched_clock_running == 2)
+ schedule_work(&sched_clock_work);
}
-void sched_clock_init(void)
+void sched_clock_init_late(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.
*
if (__sched_clock_stable_early)
__set_sched_clock_stable();
- else
- __clear_sched_clock_stable(NULL);
}
/*
* 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);
u64 clock;
if (sched_clock_stable())
- return sched_clock();
+ return sched_clock() + raw_offset;
if (unlikely(!sched_clock_running))
return 0ull;
return clock;
}
+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);
}
/*
}
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)
-{
- if (!sched_clock_stable())
- return sched_clock_cpu(cpu);
-
- return sched_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)
-{
- if (!sched_clock_stable())
- return sched_clock_cpu(raw_smp_processor_id());
-
- return sched_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 sched_clock();
}
-u64 cpu_clock(int cpu)
-{
- return sched_clock();
-}
-
-u64 local_clock(void)
-{
- return sched_clock();
-}
-
#endif /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */
-EXPORT_SYMBOL_GPL(cpu_clock);
-EXPORT_SYMBOL_GPL(local_clock);
-
/*
* Running clock - returns the time that has elapsed while a guest has been
* running.
projects / linux.git / blobdiff