From 2c3c1048746a4622d8c89a29670120dc8fab93c4 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Sun, 7 Apr 2024 20:49:45 +0200 Subject: Adding upstream version 6.1.76. Signed-off-by: Daniel Baumann --- kernel/sched/clock.c | 480 +++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 480 insertions(+) create mode 100644 kernel/sched/clock.c (limited to 'kernel/sched/clock.c') diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c new file mode 100644 index 000000000..e374c0c92 --- /dev/null +++ b/kernel/sched/clock.c @@ -0,0 +1,480 @@ +// 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 + * + * Based on code by: + * Ingo Molnar + * Guillaume Chazarain + * + * + * 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) +{ + return (unsigned long long)(jiffies - INITIAL_JIFFIES) + * (NSEC_PER_SEC / HZ); +} +EXPORT_SYMBOL_GPL(sched_clock); + +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 = 1; + +/* + * 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 { + u64 tick_raw; + u64 tick_gtod; + u64 clock; +}; + +static DEFINE_PER_CPU_SHARED_ALIGNED(struct sched_clock_data, sched_clock_data); + +notrace static inline struct sched_clock_data *this_scd(void) +{ + return this_cpu_ptr(&sched_clock_data); +} + +notrace static inline struct sched_clock_data *cpu_sdc(int cpu) +{ + return &per_cpu(sched_clock_data, cpu); +} + +notrace int sched_clock_stable(void) +{ + return static_branch_likely(&__sched_clock_stable); +} + +notrace static void __scd_stamp(struct sched_clock_data *scd) +{ + scd->tick_gtod = ktime_get_ns(); + scd->tick_raw = sched_clock(); +} + +notrace static void __set_sched_clock_stable(void) +{ + struct sched_clock_data *scd; + + /* + * Since we're still unstable and the tick is already running, we have + * to disable IRQs in order to get a consistent scd->tick* reading. + */ + local_irq_disable(); + scd = this_scd(); + /* + * Attempt to make the (initial) unstable->stable transition continuous. + */ + __sched_clock_offset = (scd->tick_gtod + __gtod_offset) - (scd->tick_raw); + local_irq_enable(); + + printk(KERN_INFO "sched_clock: Marking stable (%lld, %lld)->(%lld, %lld)\n", + scd->tick_gtod, __gtod_offset, + scd->tick_raw, __sched_clock_offset); + + static_branch_enable(&__sched_clock_stable); + tick_dep_clear(TICK_DEP_BIT_CLOCK_UNSTABLE); +} + +/* + * 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) +{ + struct sched_clock_data *scd; + int cpu; + + /* take a current timestamp and set 'now' */ + preempt_disable(); + scd = this_scd(); + __scd_stamp(scd); + scd->clock = scd->tick_gtod + __gtod_offset; + preempt_enable(); + + /* clone to all CPUs */ + for_each_possible_cpu(cpu) + per_cpu(sched_clock_data, cpu) = *scd; + + printk(KERN_WARNING "TSC found unstable after boot, most likely due to broken BIOS. Use 'tsc=unstable'.\n"); + printk(KERN_INFO "sched_clock: Marking unstable (%lld, %lld)<-(%lld, %lld)\n", + scd->tick_gtod, __gtod_offset, + scd->tick_raw, __sched_clock_offset); + + static_branch_disable(&__sched_clock_stable); +} + +static DECLARE_WORK(sched_clock_work, __sched_clock_work); + +notrace static void __clear_sched_clock_stable(void) +{ + if (!sched_clock_stable()) + return; + + tick_dep_set(TICK_DEP_BIT_CLOCK_UNSTABLE); + schedule_work(&sched_clock_work); +} + +notrace void clear_sched_clock_stable(void) +{ + __sched_clock_stable_early = 0; + + smp_mb(); /* matches sched_clock_init_late() */ + + if (static_key_count(&sched_clock_running.key) == 2) + __clear_sched_clock_stable(); +} + +notrace static void __sched_clock_gtod_offset(void) +{ + struct sched_clock_data *scd = this_scd(); + + __scd_stamp(scd); + __gtod_offset = (scd->tick_raw + __sched_clock_offset) - scd->tick_gtod; +} + +void __init sched_clock_init(void) +{ + /* + * Set __gtod_offset such that once we mark sched_clock_running, + * sched_clock_tick() continues where sched_clock() left off. + * + * Even if TSC is buggered, we're still UP at this point so it + * can't really be out of sync. + */ + local_irq_disable(); + __sched_clock_gtod_offset(); + local_irq_enable(); + + static_branch_inc(&sched_clock_running); +} +/* + * 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) +{ + static_branch_inc(&sched_clock_running); + /* + * Ensure that it is impossible to not do a static_key update. + * + * Either {set,clear}_sched_clock_stable() must see sched_clock_running + * and do the update, or we must see their __sched_clock_stable_early + * and do the update, or both. + */ + smp_mb(); /* matches {set,clear}_sched_clock_stable() */ + + if (__sched_clock_stable_early) + __set_sched_clock_stable(); + + return 0; +} +late_initcall(sched_clock_init_late); + +/* + * min, max except they take wrapping into account + */ + +notrace static inline u64 wrap_min(u64 x, u64 y) +{ + return (s64)(x - y) < 0 ? x : y; +} + +notrace static inline u64 wrap_max(u64 x, u64 y) +{ + return (s64)(x - y) > 0 ? x : 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 + */ +notrace static u64 sched_clock_local(struct sched_clock_data *scd) +{ + u64 now, clock, old_clock, min_clock, max_clock, gtod; + s64 delta; + +again: + now = sched_clock(); + delta = now - scd->tick_raw; + if (unlikely(delta < 0)) + delta = 0; + + old_clock = scd->clock; + + /* + * scd->clock = clamp(scd->tick_gtod + delta, + * max(scd->tick_gtod, scd->clock), + * scd->tick_gtod + TICK_NSEC); + */ + + gtod = scd->tick_gtod + __gtod_offset; + clock = gtod + delta; + min_clock = wrap_max(gtod, old_clock); + max_clock = wrap_max(old_clock, gtod + TICK_NSEC); + + clock = wrap_max(clock, min_clock); + clock = wrap_min(clock, max_clock); + + if (!try_cmpxchg64(&scd->clock, &old_clock, clock)) + goto again; + + return clock; +} + +notrace static u64 sched_clock_remote(struct sched_clock_data *scd) +{ + struct sched_clock_data *my_scd = this_scd(); + u64 this_clock, remote_clock; + u64 *ptr, old_val, val; + +#if BITS_PER_LONG != 64 +again: + /* + * Careful here: The local and the remote clock values need to + * be read out atomic as we need to compare the values and + * then update either the local or the remote side. So the + * cmpxchg64 below only protects one readout. + * + * We must reread via sched_clock_local() in the retry case on + * 32-bit kernels as an NMI could use sched_clock_local() via the + * tracer and hit between the readout of + * the low 32-bit and the high 32-bit portion. + */ + this_clock = sched_clock_local(my_scd); + /* + * We must enforce atomic readout on 32-bit, otherwise the + * update on the remote CPU can hit inbetween the readout of + * the low 32-bit and the high 32-bit portion. + */ + remote_clock = cmpxchg64(&scd->clock, 0, 0); +#else + /* + * On 64-bit kernels the read of [my]scd->clock is atomic versus the + * update, so we can avoid the above 32-bit dance. + */ + sched_clock_local(my_scd); +again: + this_clock = my_scd->clock; + remote_clock = scd->clock; +#endif + + /* + * 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)) { + ptr = &scd->clock; + old_val = remote_clock; + val = this_clock; + } else { + /* + * Should be rare, but possible: + */ + ptr = &my_scd->clock; + old_val = this_clock; + val = remote_clock; + } + + if (!try_cmpxchg64(ptr, &old_val, val)) + goto again; + + return val; +} + +/* + * Similar to cpu_clock(), but requires local IRQs to be disabled. + * + * See cpu_clock(). + */ +notrace u64 sched_clock_cpu(int cpu) +{ + struct sched_clock_data *scd; + u64 clock; + + if (sched_clock_stable()) + return sched_clock() + __sched_clock_offset; + + if (!static_branch_likely(&sched_clock_running)) + return sched_clock(); + + preempt_disable_notrace(); + scd = cpu_sdc(cpu); + + if (cpu != smp_processor_id()) + clock = sched_clock_remote(scd); + else + clock = sched_clock_local(scd); + preempt_enable_notrace(); + + return clock; +} +EXPORT_SYMBOL_GPL(sched_clock_cpu); + +notrace void sched_clock_tick(void) +{ + struct sched_clock_data *scd; + + if (sched_clock_stable()) + return; + + if (!static_branch_likely(&sched_clock_running)) + return; + + lockdep_assert_irqs_disabled(); + + scd = this_scd(); + __scd_stamp(scd); + sched_clock_local(scd); +} + +notrace void sched_clock_tick_stable(void) +{ + if (!sched_clock_stable()) + return; + + /* + * Called under watchdog_lock. + * + * The watchdog just found this TSC to (still) be stable, so now is a + * good moment to update our __gtod_offset. Because once we find the + * TSC to be unstable, any computation will be computing crap. + */ + local_irq_disable(); + __sched_clock_gtod_offset(); + local_irq_enable(); +} + +/* + * We are going deep-idle (irqs are disabled): + */ +notrace void sched_clock_idle_sleep_event(void) +{ + sched_clock_cpu(smp_processor_id()); +} +EXPORT_SYMBOL_GPL(sched_clock_idle_sleep_event); + +/* + * We just idled; resync with ktime. + */ +notrace void sched_clock_idle_wakeup_event(void) +{ + unsigned long flags; + + if (sched_clock_stable()) + return; + + if (unlikely(timekeeping_suspended)) + return; + + local_irq_save(flags); + sched_clock_tick(); + local_irq_restore(flags); +} +EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event); + +#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) +{ + return local_clock(); +} -- cgit v1.2.3