--- /dev/null
+/*
+ * sched_clock for unstable cpu clocks
+ *
+ * Copyright (C) 2008 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
+ *
+ * Updates and enhancements:
+ * Copyright (C) 2008 Red Hat, Inc. Steven Rostedt <srostedt@redhat.com>
+ *
+ * Based on code by:
+ * Ingo Molnar <mingo@redhat.com>
+ * Guillaume Chazarain <guichaz@gmail.com>
+ *
+ *
+ * What:
+ *
+ * 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:
+ *
+ * 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 monotomic)
+ * - 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).
+ *
+ */
+#include <linux/spinlock.h>
+#include <linux/hardirq.h>
+#include <linux/export.h>
+#include <linux/percpu.h>
+#include <linux/ktime.h>
+#include <linux/sched.h>
+#include <linux/static_key.h>
+#include <linux/workqueue.h>
+#include <linux/compiler.h>
+
+/*
+ * Scheduler clock - returns current time in nanosec units.
+ * This is default implementation.
+ * Architectures and sub-architectures can override this.
+ */
+unsigned long long __weak sched_clock(void)
+{
+ return (unsigned long long)(jiffies - INITIAL_JIFFIES)
+ * (NSEC_PER_SEC / HZ);
+}
+EXPORT_SYMBOL_GPL(sched_clock);
+
+__read_mostly int sched_clock_running;
+
+#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
+static struct static_key __sched_clock_stable = STATIC_KEY_INIT;
+static int __sched_clock_stable_early;
+
+int sched_clock_stable(void)
+{
+ return static_key_false(&__sched_clock_stable);
+}
+
+static void __set_sched_clock_stable(void)
+{
+ if (!sched_clock_stable())
+ static_key_slow_inc(&__sched_clock_stable);
+}
+
+void set_sched_clock_stable(void)
+{
+ __sched_clock_stable_early = 1;
+
+ smp_mb(); /* matches sched_clock_init() */
+
+ if (!sched_clock_running)
+ return;
+
+ __set_sched_clock_stable();
+}
+
+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);
+}
+
+static DECLARE_WORK(sched_clock_work, __clear_sched_clock_stable);
+
+void clear_sched_clock_stable(void)
+{
+ __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);
+}
+
+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;
+
+ /*
+ * 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();
+ else
+ __clear_sched_clock_stable(NULL);
+}
+
+/*
+ * min, max except they take wrapping into account
+ */
+
+static inline u64 wrap_min(u64 x, u64 y)
+{
+ return (s64)(x - y) < 0 ? x : y;
+}
+
+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
+ */
+static u64 sched_clock_local(struct sched_clock_data *scd)
+{
+ u64 now, clock, old_clock, min_clock, max_clock;
+ 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);
+ */
+
+ clock = scd->tick_gtod + delta;
+ min_clock = wrap_max(scd->tick_gtod, old_clock);
+ max_clock = wrap_max(old_clock, scd->tick_gtod + TICK_NSEC);
+
+ clock = wrap_max(clock, min_clock);
+ clock = wrap_min(clock, max_clock);
+
+ if (cmpxchg64(&scd->clock, old_clock, clock) != old_clock)
+ goto again;
+
+ return clock;
+}
+
+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
+ * 32bit as an NMI could use sched_clock_local() via the
+ * tracer and hit between the readout of
+ * the low32bit and the high 32bit portion.
+ */
+ this_clock = sched_clock_local(my_scd);
+ /*
+ * We must enforce atomic readout on 32bit, otherwise the
+ * update on the remote cpu can hit inbetween the readout of
+ * the low32bit and the high 32bit portion.
+ */
+ remote_clock = cmpxchg64(&scd->clock, 0, 0);
+#else
+ /*
+ * On 64bit the read of [my]scd->clock is atomic versus the
+ * update, so we can avoid the above 32bit 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 (cmpxchg64(ptr, old_val, val) != old_val)
+ goto again;
+
+ return val;
+}
+
+/*
+ * Similar to cpu_clock(), but requires local IRQs to be disabled.
+ *
+ * See cpu_clock().
+ */
+u64 sched_clock_cpu(int cpu)
+{
+ struct sched_clock_data *scd;
+ u64 clock;
+
+ if (sched_clock_stable())
+ return sched_clock();
+
+ if (unlikely(!sched_clock_running))
+ return 0ull;
+
+ 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;
+}
+
+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());
+
+ scd = this_scd();
+ now_gtod = ktime_to_ns(ktime_get());
+ now = sched_clock();
+
+ scd->tick_raw = now;
+ scd->tick_gtod = now_gtod;
+ sched_clock_local(scd);
+}
+
+/*
+ * We are going deep-idle (irqs are disabled):
+ */
+void sched_clock_idle_sleep_event(void)
+{
+ sched_clock_cpu(smp_processor_id());
+}
+EXPORT_SYMBOL_GPL(sched_clock_idle_sleep_event);
+
+/*
+ * We just idled delta nanoseconds (called with irqs disabled):
+ */
+void sched_clock_idle_wakeup_event(u64 delta_ns)
+{
+ if (timekeeping_suspended)
+ return;
+
+ sched_clock_tick();
+ touch_softlockup_watchdog();
+}
+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 0;
+
+ 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.
+ * 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.
+ */
+u64 __weak running_clock(void)
+{
+ return local_clock();
+}
Code Review / kvmfornfv.git / blobdiff