linux/kernel/sched/clock.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * sched_clock() for unstable CPU clocks
 *
 *  Copyright (C) 2008 Red Hat, Inc., Peter Zijlstra
 *
 *  Updates and enhancements:
 *    Copyright (C) 2008 Red Hat, Inc. Steven Rostedt <[email protected]>
 *
 * Based on code by:
 *   Ingo Molnar <[email protected]>
 *   Guillaume Chazarain <[email protected]>
 *
 *
 * What this file implements:
 *
 * 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.
 * local_clock()      -- is cpu_clock() on the current CPU.
 *
 * sched_clock_cpu(i)
 *
 * How it is implemented:
 *
 * 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 monotonic)
 *  - 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).
 *
 */

/*
 * Scheduler clock - returns current time in nanosec units.
 * This is default implementation.
 * Architectures and sub-architectures can override this.
 */
notrace unsigned long long __weak sched_clock(void)
{}
EXPORT_SYMBOL_GPL();

static DEFINE_STATIC_KEY_FALSE(sched_clock_running);

#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
/*
 * 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 =;

/*
 * We want: ktime_get_ns() + __gtod_offset == sched_clock() + __sched_clock_offset
 */
__read_mostly u64 __sched_clock_offset;
static __read_mostly u64 __gtod_offset;

struct sched_clock_data {};

static DEFINE_PER_CPU_SHARED_ALIGNED(struct sched_clock_data, sched_clock_data);

static __always_inline struct sched_clock_data *this_scd(void)
{}

notrace static inline struct sched_clock_data *cpu_sdc(int cpu)
{}

notrace int sched_clock_stable(void)
{}

notrace static void __scd_stamp(struct sched_clock_data *scd)
{}

notrace static void __set_sched_clock_stable(void)
{}

/*
 * If we ever get here, we're screwed, because we found out -- typically after
 * the fact -- that TSC wasn't good. This means all our clocksources (including
 * ktime) could have reported wrong values.
 *
 * What we do here is an attempt to fix up and continue sort of where we left
 * off in a coherent manner.
 *
 * The only way to fully avoid random clock jumps is to boot with:
 * "tsc=unstable".
 */
notrace static void __sched_clock_work(struct work_struct *work)
{}

static DECLARE_WORK(sched_clock_work, __sched_clock_work);

notrace static void __clear_sched_clock_stable(void)
{}

notrace void clear_sched_clock_stable(void)
{}

notrace static void __sched_clock_gtod_offset(void)
{}

void __init sched_clock_init(void)
{}
/*
 * We run this as late_initcall() such that it runs after all built-in drivers,
 * notably: acpi_processor and intel_idle, which can mark the TSC as unstable.
 */
static int __init sched_clock_init_late(void)
{}
late_initcall(sched_clock_init_late);

/*
 * min, max except they take wrapping into account
 */

static __always_inline u64 wrap_min(u64 x, u64 y)
{}

static __always_inline u64 wrap_max(u64 x, u64 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 __always_inline u64 sched_clock_local(struct sched_clock_data *scd)
{}

noinstr u64 local_clock_noinstr(void)
{}

u64 local_clock(void)
{}
EXPORT_SYMBOL_GPL();

static notrace u64 sched_clock_remote(struct sched_clock_data *scd)
{}

/*
 * Similar to cpu_clock(), but requires local IRQs to be disabled.
 *
 * See cpu_clock().
 */
notrace u64 sched_clock_cpu(int cpu)
{}
EXPORT_SYMBOL_GPL();

notrace void sched_clock_tick(void)
{}

notrace void sched_clock_tick_stable(void)
{}

/*
 * We are going deep-idle (IRQs are disabled):
 */
notrace void sched_clock_idle_sleep_event(void)
{}
EXPORT_SYMBOL_GPL();

/*
 * We just idled; resync with ktime.
 */
notrace void sched_clock_idle_wakeup_event(void)
{}
EXPORT_SYMBOL_GPL();

#else /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */

void __init sched_clock_init(void)
{
	static_branch_inc(&sched_clock_running);
	local_irq_disable();
	generic_sched_clock_init();
	local_irq_enable();
}

notrace u64 sched_clock_cpu(int cpu)
{
	if (!static_branch_likely(&sched_clock_running))
		return 0;

	return sched_clock();
}

#endif /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */

/*
 * Running clock - returns the time that has elapsed while a guest has been
 * running.
 * On a guest this value should be local_clock minus the time the guest was
 * suspended by the hypervisor (for any reason).
 * On bare metal this function should return the same as local_clock.
 * Architectures and sub-architectures can override this.
 */
notrace u64 __weak running_clock(void)
{}