102 lines
2.5 KiB
C
102 lines
2.5 KiB
C
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/*
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* tracing clocks
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*
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* Copyright (C) 2009 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
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*
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* Implements 3 trace clock variants, with differing scalability/precision
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* tradeoffs:
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*
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* - local: CPU-local trace clock
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* - medium: scalable global clock with some jitter
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* - global: globally monotonic, serialized clock
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*
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* Tracer plugins will chose a default from these clocks.
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*/
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#include <linux/spinlock.h>
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#include <linux/hardirq.h>
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#include <linux/module.h>
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#include <linux/percpu.h>
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#include <linux/sched.h>
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#include <linux/ktime.h>
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/*
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* trace_clock_local(): the simplest and least coherent tracing clock.
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*
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* Useful for tracing that does not cross to other CPUs nor
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* does it go through idle events.
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*/
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u64 notrace trace_clock_local(void)
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{
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/*
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* sched_clock() is an architecture implemented, fast, scalable,
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* lockless clock. It is not guaranteed to be coherent across
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* CPUs, nor across CPU idle events.
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*/
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return sched_clock();
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}
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/*
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* trace_clock(): 'inbetween' trace clock. Not completely serialized,
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* but not completely incorrect when crossing CPUs either.
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*
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* This is based on cpu_clock(), which will allow at most ~1 jiffy of
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* jitter between CPUs. So it's a pretty scalable clock, but there
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* can be offsets in the trace data.
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*/
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u64 notrace trace_clock(void)
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{
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return cpu_clock(raw_smp_processor_id());
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}
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/*
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* trace_clock_global(): special globally coherent trace clock
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*
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* It has higher overhead than the other trace clocks but is still
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* an order of magnitude faster than GTOD derived hardware clocks.
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*
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* Used by plugins that need globally coherent timestamps.
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*/
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static u64 prev_trace_clock_time;
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static raw_spinlock_t trace_clock_lock ____cacheline_aligned_in_smp =
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(raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED;
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u64 notrace trace_clock_global(void)
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{
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unsigned long flags;
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int this_cpu;
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u64 now;
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raw_local_irq_save(flags);
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this_cpu = raw_smp_processor_id();
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now = cpu_clock(this_cpu);
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/*
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* If in an NMI context then dont risk lockups and return the
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* cpu_clock() time:
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*/
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if (unlikely(in_nmi()))
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goto out;
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__raw_spin_lock(&trace_clock_lock);
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/*
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* TODO: if this happens often then maybe we should reset
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* my_scd->clock to prev_trace_clock_time+1, to make sure
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* we start ticking with the local clock from now on?
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*/
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if ((s64)(now - prev_trace_clock_time) < 0)
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now = prev_trace_clock_time + 1;
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prev_trace_clock_time = now;
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__raw_spin_unlock(&trace_clock_lock);
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out:
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raw_local_irq_restore(flags);
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return now;
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}
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