sched_clock: Make it NMI safe
Arjan complained about the suckyness of TSC on modern machines, and asked if we could do something about that for PERF_SAMPLE_TIME. Make cpu_clock() NMI safe by removing the spinlock and using cmpxchg. This also makes it smaller and more robust. Affects architectures that use HAVE_UNSTABLE_SCHED_CLOCK, i.e. IA64 and x86. Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <new-submission> Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Peter Zijlstra
Ingo Molnar
Родитель
cf450a7355
Коммит
def0a9b257
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@ -2955,10 +2955,7 @@ void perf_prepare_sample(struct perf_event_header *header,
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}
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if (sample_type & PERF_SAMPLE_TIME) {
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/*
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* Maybe do better on x86 and provide cpu_clock_nmi()
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*/
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data->time = sched_clock();
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data->time = perf_clock();
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header->size += sizeof(data->time);
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}
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@ -3488,7 +3485,7 @@ static void perf_log_throttle(struct perf_counter *counter, int enable)
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.misc = 0,
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.size = sizeof(throttle_event),
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},
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.time = sched_clock(),
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.time = perf_clock(),
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.id = primary_counter_id(counter),
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.stream_id = counter->id,
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};
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@ -3540,7 +3537,7 @@ static int __perf_counter_overflow(struct perf_counter *counter, int nmi,
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}
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if (counter->attr.freq) {
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u64 now = sched_clock();
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u64 now = perf_clock();
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s64 delta = now - hwc->freq_stamp;
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hwc->freq_stamp = now;
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@ -48,13 +48,6 @@ static __read_mostly int sched_clock_running;
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__read_mostly int sched_clock_stable;
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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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u64 tick_raw;
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u64 tick_gtod;
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u64 clock;
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@ -80,7 +73,6 @@ void sched_clock_init(void)
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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_raw = 0;
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scd->tick_gtod = ktime_now;
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scd->clock = ktime_now;
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@ -109,14 +101,19 @@ static inline u64 wrap_max(u64 x, u64 y)
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* - filter out backward motion
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* - use the GTOD tick value to create a window to filter crazy TSC values
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*/
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static u64 __update_sched_clock(struct sched_clock_data *scd, u64 now)
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static u64 sched_clock_local(struct sched_clock_data *scd)
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{
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s64 delta = now - scd->tick_raw;
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u64 clock, min_clock, max_clock;
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u64 now, clock, old_clock, min_clock, max_clock;
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s64 delta;
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again:
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now = sched_clock();
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delta = now - scd->tick_raw;
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if (unlikely(delta < 0))
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delta = 0;
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old_clock = scd->clock;
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/*
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* scd->clock = clamp(scd->tick_gtod + delta,
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* max(scd->tick_gtod, scd->clock),
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@ -124,84 +121,73 @@ static u64 __update_sched_clock(struct sched_clock_data *scd, u64 now)
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*/
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clock = scd->tick_gtod + delta;
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min_clock = wrap_max(scd->tick_gtod, scd->clock);
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max_clock = wrap_max(scd->clock, scd->tick_gtod + TICK_NSEC);
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min_clock = wrap_max(scd->tick_gtod, old_clock);
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max_clock = wrap_max(old_clock, scd->tick_gtod + TICK_NSEC);
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clock = wrap_max(clock, min_clock);
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clock = wrap_min(clock, max_clock);
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scd->clock = clock;
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if (cmpxchg(&scd->clock, old_clock, clock) != old_clock)
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goto again;
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return scd->clock;
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return clock;
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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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static u64 sched_clock_remote(struct sched_clock_data *scd)
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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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struct sched_clock_data *my_scd = this_scd();
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u64 this_clock, remote_clock;
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u64 *ptr, old_val, val;
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sched_clock_local(my_scd);
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again:
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this_clock = my_scd->clock;
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remote_clock = scd->clock;
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/*
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* Use the opportunity that we have both locks
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* taken to couple the two clocks: we take the
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* larger time as the latest time for both
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* runqueues. (this creates monotonic movement)
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*/
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if (likely((s64)(remote_clock - this_clock) < 0)) {
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ptr = &scd->clock;
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old_val = remote_clock;
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val = this_clock;
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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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* Should be rare, but possible:
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*/
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ptr = &my_scd->clock;
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old_val = this_clock;
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val = remote_clock;
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}
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if (cmpxchg(ptr, old_val, val) != old_val)
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goto again;
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return val;
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}
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u64 sched_clock_cpu(int cpu)
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{
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u64 now, clock, this_clock, remote_clock;
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struct sched_clock_data *scd;
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u64 clock;
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WARN_ON_ONCE(!irqs_disabled());
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if (sched_clock_stable)
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return sched_clock();
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scd = cpu_sdc(cpu);
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/*
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* Normally this is not called in NMI context - but if it is,
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* trying to do any locking here is totally lethal.
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*/
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if (unlikely(in_nmi()))
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return scd->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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scd = cpu_sdc(cpu);
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if (cpu != raw_smp_processor_id()) {
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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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this_clock = __update_sched_clock(my_scd, now);
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remote_clock = scd->clock;
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/*
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* Use the opportunity that we have both locks
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* taken to couple the two clocks: we take the
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* larger time as the latest time for both
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* runqueues. (this creates monotonic movement)
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*/
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if (likely((s64)(remote_clock - this_clock) < 0)) {
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clock = this_clock;
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scd->clock = clock;
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} else {
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/*
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* Should be rare, but possible:
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*/
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clock = remote_clock;
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my_scd->clock = remote_clock;
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}
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__raw_spin_unlock(&my_scd->lock);
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} else {
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__raw_spin_lock(&scd->lock);
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clock = __update_sched_clock(scd, now);
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}
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__raw_spin_unlock(&scd->lock);
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if (cpu != smp_processor_id())
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clock = sched_clock_remote(scd);
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else
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clock = sched_clock_local(scd);
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return clock;
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}
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@ -223,11 +209,9 @@ void sched_clock_tick(void)
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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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scd->tick_raw = now;
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scd->tick_gtod = now_gtod;
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__update_sched_clock(scd, now);
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__raw_spin_unlock(&scd->lock);
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sched_clock_local(scd);
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}
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/*
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