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https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
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345 lines
7.7 KiB
C
345 lines
7.7 KiB
C
/*
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* sched_clock for unstable cpu clocks
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*
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* Copyright (C) 2008 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
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*
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* Updates and enhancements:
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* Copyright (C) 2008 Red Hat, Inc. Steven Rostedt <srostedt@redhat.com>
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*
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* Based on code by:
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* Ingo Molnar <mingo@redhat.com>
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* Guillaume Chazarain <guichaz@gmail.com>
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*
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* Create a semi stable clock from a mixture of other events, including:
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* - gtod
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* - jiffies
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* - sched_clock()
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* - explicit idle events
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*
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* We use gtod as base and the unstable clock deltas. The deltas are filtered,
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* making it monotonic and keeping it within an expected window. This window
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* is set up using jiffies.
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*
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* Furthermore, explicit sleep and wakeup hooks allow us to account for time
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* that is otherwise invisible (TSC gets stopped).
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*
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* The clock: sched_clock_cpu() is monotonic per cpu, and should be somewhat
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* consistent between cpus (never more than 1 jiffies difference).
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*/
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#include <linux/sched.h>
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#include <linux/percpu.h>
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#include <linux/spinlock.h>
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#include <linux/ktime.h>
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#include <linux/module.h>
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#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
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#define MULTI_SHIFT 15
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/* Max is double, Min is 1/2 */
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#define MAX_MULTI (2LL << MULTI_SHIFT)
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#define MIN_MULTI (1LL << (MULTI_SHIFT-1))
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struct sched_clock_data {
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/*
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* Raw spinlock - this is a special case: this might be called
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* from within instrumentation code so we dont want to do any
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* instrumentation ourselves.
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*/
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raw_spinlock_t lock;
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unsigned long tick_jiffies;
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u64 prev_raw;
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u64 tick_raw;
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u64 tick_gtod;
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u64 clock;
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s64 multi;
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#ifdef CONFIG_NO_HZ
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int check_max;
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#endif
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};
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static DEFINE_PER_CPU_SHARED_ALIGNED(struct sched_clock_data, sched_clock_data);
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static inline struct sched_clock_data *this_scd(void)
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{
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return &__get_cpu_var(sched_clock_data);
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}
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static inline struct sched_clock_data *cpu_sdc(int cpu)
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{
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return &per_cpu(sched_clock_data, cpu);
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}
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static __read_mostly int sched_clock_running;
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void sched_clock_init(void)
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{
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u64 ktime_now = ktime_to_ns(ktime_get());
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unsigned long now_jiffies = jiffies;
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int cpu;
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for_each_possible_cpu(cpu) {
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struct sched_clock_data *scd = cpu_sdc(cpu);
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scd->lock = (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED;
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scd->tick_jiffies = now_jiffies;
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scd->prev_raw = 0;
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scd->tick_raw = 0;
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scd->tick_gtod = ktime_now;
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scd->clock = ktime_now;
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scd->multi = 1 << MULTI_SHIFT;
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#ifdef CONFIG_NO_HZ
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scd->check_max = 1;
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#endif
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}
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sched_clock_running = 1;
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}
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#ifdef CONFIG_NO_HZ
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/*
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* The dynamic ticks makes the delta jiffies inaccurate. This
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* prevents us from checking the maximum time update.
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* Disable the maximum check during stopped ticks.
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*/
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void sched_clock_tick_stop(int cpu)
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{
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struct sched_clock_data *scd = cpu_sdc(cpu);
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scd->check_max = 0;
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}
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void sched_clock_tick_start(int cpu)
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{
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struct sched_clock_data *scd = cpu_sdc(cpu);
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scd->check_max = 1;
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}
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static int check_max(struct sched_clock_data *scd)
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{
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return scd->check_max;
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}
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#else
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static int check_max(struct sched_clock_data *scd)
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{
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return 1;
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}
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#endif /* CONFIG_NO_HZ */
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/*
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* update the percpu scd from the raw @now value
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*
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* - filter out backward motion
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* - use jiffies to generate a min,max window to clip the raw values
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*/
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static void __update_sched_clock(struct sched_clock_data *scd, u64 now, u64 *time)
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{
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unsigned long now_jiffies = jiffies;
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long delta_jiffies = now_jiffies - scd->tick_jiffies;
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u64 clock = scd->clock;
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u64 min_clock, max_clock;
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s64 delta = now - scd->prev_raw;
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WARN_ON_ONCE(!irqs_disabled());
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/*
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* At schedule tick the clock can be just under the gtod. We don't
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* want to push it too prematurely.
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*/
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min_clock = scd->tick_gtod + (delta_jiffies * TICK_NSEC);
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if (min_clock > TICK_NSEC)
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min_clock -= TICK_NSEC / 2;
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if (unlikely(delta < 0)) {
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clock++;
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goto out;
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}
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/*
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* The clock must stay within a jiffie of the gtod.
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* But since we may be at the start of a jiffy or the end of one
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* we add another jiffy buffer.
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*/
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max_clock = scd->tick_gtod + (2 + delta_jiffies) * TICK_NSEC;
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delta *= scd->multi;
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delta >>= MULTI_SHIFT;
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if (unlikely(clock + delta > max_clock) && check_max(scd)) {
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if (clock < max_clock)
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clock = max_clock;
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else
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clock++;
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} else {
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clock += delta;
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}
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out:
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if (unlikely(clock < min_clock))
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clock = min_clock;
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if (time)
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*time = clock;
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else {
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scd->prev_raw = now;
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scd->clock = clock;
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}
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}
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static void lock_double_clock(struct sched_clock_data *data1,
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struct sched_clock_data *data2)
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{
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if (data1 < data2) {
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__raw_spin_lock(&data1->lock);
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__raw_spin_lock(&data2->lock);
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} else {
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__raw_spin_lock(&data2->lock);
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__raw_spin_lock(&data1->lock);
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}
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}
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u64 sched_clock_cpu(int cpu)
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{
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struct sched_clock_data *scd = cpu_sdc(cpu);
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u64 now, clock;
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if (unlikely(!sched_clock_running))
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return 0ull;
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WARN_ON_ONCE(!irqs_disabled());
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now = sched_clock();
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if (cpu != raw_smp_processor_id()) {
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/*
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* in order to update a remote cpu's clock based on our
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* unstable raw time rebase it against:
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* tick_raw (offset between raw counters)
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* tick_gotd (tick offset between cpus)
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*/
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struct sched_clock_data *my_scd = this_scd();
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lock_double_clock(scd, my_scd);
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now -= my_scd->tick_raw;
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now += scd->tick_raw;
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now += my_scd->tick_gtod;
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now -= scd->tick_gtod;
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__raw_spin_unlock(&my_scd->lock);
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__update_sched_clock(scd, now, &clock);
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__raw_spin_unlock(&scd->lock);
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} else {
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__raw_spin_lock(&scd->lock);
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__update_sched_clock(scd, now, NULL);
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clock = scd->clock;
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__raw_spin_unlock(&scd->lock);
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}
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return clock;
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}
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void sched_clock_tick(void)
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{
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struct sched_clock_data *scd = this_scd();
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unsigned long now_jiffies = jiffies;
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s64 mult, delta_gtod, delta_raw;
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u64 now, now_gtod;
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if (unlikely(!sched_clock_running))
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return;
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WARN_ON_ONCE(!irqs_disabled());
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now_gtod = ktime_to_ns(ktime_get());
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now = sched_clock();
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__raw_spin_lock(&scd->lock);
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__update_sched_clock(scd, now, NULL);
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/*
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* update tick_gtod after __update_sched_clock() because that will
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* already observe 1 new jiffy; adding a new tick_gtod to that would
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* increase the clock 2 jiffies.
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*/
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delta_gtod = now_gtod - scd->tick_gtod;
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delta_raw = now - scd->tick_raw;
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if ((long)delta_raw > 0) {
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mult = delta_gtod << MULTI_SHIFT;
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do_div(mult, delta_raw);
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scd->multi = mult;
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if (scd->multi > MAX_MULTI)
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scd->multi = MAX_MULTI;
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else if (scd->multi < MIN_MULTI)
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scd->multi = MIN_MULTI;
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} else
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scd->multi = 1 << MULTI_SHIFT;
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scd->tick_raw = now;
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scd->tick_gtod = now_gtod;
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scd->tick_jiffies = now_jiffies;
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__raw_spin_unlock(&scd->lock);
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}
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/*
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* We are going deep-idle (irqs are disabled):
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*/
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void sched_clock_idle_sleep_event(void)
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{
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sched_clock_cpu(smp_processor_id());
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}
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EXPORT_SYMBOL_GPL(sched_clock_idle_sleep_event);
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/*
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* We just idled delta nanoseconds (called with irqs disabled):
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*/
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void sched_clock_idle_wakeup_event(u64 delta_ns)
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{
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struct sched_clock_data *scd = this_scd();
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u64 now = sched_clock();
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/*
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* Override the previous timestamp and ignore all
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* sched_clock() deltas that occured while we idled,
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* and use the PM-provided delta_ns to advance the
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* rq clock:
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*/
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__raw_spin_lock(&scd->lock);
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scd->prev_raw = now;
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scd->clock += delta_ns;
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scd->multi = 1 << MULTI_SHIFT;
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__raw_spin_unlock(&scd->lock);
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touch_softlockup_watchdog();
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}
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EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);
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#endif
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/*
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* Scheduler clock - returns current time in nanosec units.
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* This is default implementation.
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* Architectures and sub-architectures can override this.
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*/
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unsigned long long __attribute__((weak)) sched_clock(void)
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{
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return (unsigned long long)jiffies * (NSEC_PER_SEC / HZ);
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}
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unsigned long long cpu_clock(int cpu)
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{
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unsigned long long clock;
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unsigned long flags;
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local_irq_save(flags);
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clock = sched_clock_cpu(cpu);
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local_irq_restore(flags);
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return clock;
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}
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EXPORT_SYMBOL_GPL(cpu_clock);
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