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sched: fix cpu clock
David Miller pointed it out that nothing in cpu_clock() sets prev_cpu_time. This caused __sync_cpu_clock() to be called all the time - against the intention of this code. The result was that in practice we hit a global spinlock every time cpu_clock() is called - which - even though cpu_clock() is used for tracing and debugging, is suboptimal. While at it, also: - move the irq disabling to the outest layer, this should make cpu_clock() warp-free when called with irqs enabled. - use long long instead of cycles_t - for platforms where cycles_t is 32-bit. Reported-by: David Miller <davem@davemloft.net> Signed-off-by: Ingo Molnar <mingo@elte.hu>
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cb4ad1ffc7
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1 changed files with 15 additions and 9 deletions
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@ -910,11 +910,14 @@ static DEFINE_PER_CPU(unsigned long long, prev_cpu_time);
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static DEFINE_SPINLOCK(time_sync_lock);
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static unsigned long long prev_global_time;
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static unsigned long long __sync_cpu_clock(cycles_t time, int cpu)
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static unsigned long long __sync_cpu_clock(unsigned long long time, int cpu)
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{
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unsigned long flags;
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spin_lock_irqsave(&time_sync_lock, flags);
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/*
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* We want this inlined, to not get tracer function calls
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* in this critical section:
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*/
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spin_acquire(&time_sync_lock.dep_map, 0, 0, _THIS_IP_);
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__raw_spin_lock(&time_sync_lock.raw_lock);
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if (time < prev_global_time) {
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per_cpu(time_offset, cpu) += prev_global_time - time;
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@ -923,7 +926,8 @@ static unsigned long long __sync_cpu_clock(cycles_t time, int cpu)
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prev_global_time = time;
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}
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spin_unlock_irqrestore(&time_sync_lock, flags);
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__raw_spin_unlock(&time_sync_lock.raw_lock);
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spin_release(&time_sync_lock.dep_map, 1, _THIS_IP_);
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return time;
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}
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@ -931,7 +935,6 @@ static unsigned long long __sync_cpu_clock(cycles_t time, int cpu)
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static unsigned long long __cpu_clock(int cpu)
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{
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unsigned long long now;
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unsigned long flags;
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struct rq *rq;
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/*
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@ -941,11 +944,9 @@ static unsigned long long __cpu_clock(int cpu)
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if (unlikely(!scheduler_running))
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return 0;
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local_irq_save(flags);
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rq = cpu_rq(cpu);
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update_rq_clock(rq);
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now = rq->clock;
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local_irq_restore(flags);
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return now;
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}
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@ -957,13 +958,18 @@ static unsigned long long __cpu_clock(int cpu)
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unsigned long long cpu_clock(int cpu)
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{
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unsigned long long prev_cpu_time, time, delta_time;
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unsigned long flags;
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local_irq_save(flags);
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prev_cpu_time = per_cpu(prev_cpu_time, cpu);
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time = __cpu_clock(cpu) + per_cpu(time_offset, cpu);
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delta_time = time-prev_cpu_time;
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if (unlikely(delta_time > time_sync_thresh))
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if (unlikely(delta_time > time_sync_thresh)) {
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time = __sync_cpu_clock(time, cpu);
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per_cpu(prev_cpu_time, cpu) = time;
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}
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local_irq_restore(flags);
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return time;
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}
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