sched clock: couple local and remote clocks
When taking the time of a remote CPU, use the opportunity to couple (sync) the clocks to each other. (in a monotonic way) Signed-off-by: Ingo Molnar <mingo@elte.hu> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Acked-by: Mike Galbraith <efault@gmx.de>
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@ -149,7 +149,7 @@ static void lock_double_clock(struct sched_clock_data *data1,
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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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u64 now, clock, this_clock, remote_clock;
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if (unlikely(!sched_clock_running))
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return 0ull;
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@ -158,25 +158,35 @@ u64 sched_clock_cpu(int cpu)
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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 += scd->tick_raw - my_scd->tick_raw;
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now += my_scd->tick_gtod - scd->tick_gtod;
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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(remote_clock < this_clock)) {
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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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}
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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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@ -223,7 +233,6 @@ EXPORT_SYMBOL_GPL(sched_clock_idle_sleep_event);
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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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