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kernel/trace/trace_clock.c
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/* * tracing clocks * * Copyright (C) 2009 Red Hat, Inc., Ingo Molnar <mingo@redhat.com> * * Implements 3 trace clock variants, with differing scalability/precision * tradeoffs: * * - local: CPU-local trace clock * - medium: scalable global clock with some jitter * - global: globally monotonic, serialized clock * * Tracer plugins will chose a default from these clocks. */ #include <linux/spinlock.h> |
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#include <linux/irqflags.h> |
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#include <linux/hardirq.h> #include <linux/module.h> #include <linux/percpu.h> #include <linux/sched.h> #include <linux/ktime.h> |
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#include <linux/trace_clock.h> |
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#include "trace.h" |
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/* * trace_clock_local(): the simplest and least coherent tracing clock. * * Useful for tracing that does not cross to other CPUs nor * does it go through idle events. */ u64 notrace trace_clock_local(void) { |
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u64 clock; |
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/* * sched_clock() is an architecture implemented, fast, scalable, * lockless clock. It is not guaranteed to be coherent across * CPUs, nor across CPU idle events. */ |
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preempt_disable_notrace(); |
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clock = sched_clock(); |
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preempt_enable_notrace(); |
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return clock; |
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} /* |
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* trace_clock(): 'between' trace clock. Not completely serialized, |
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* but not completely incorrect when crossing CPUs either. * * This is based on cpu_clock(), which will allow at most ~1 jiffy of * jitter between CPUs. So it's a pretty scalable clock, but there * can be offsets in the trace data. */ u64 notrace trace_clock(void) { |
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return local_clock(); |
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} /* * trace_clock_global(): special globally coherent trace clock * * It has higher overhead than the other trace clocks but is still * an order of magnitude faster than GTOD derived hardware clocks. * * Used by plugins that need globally coherent timestamps. */ |
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/* keep prev_time and lock in the same cacheline. */ static struct { u64 prev_time; |
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arch_spinlock_t lock; |
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} trace_clock_struct ____cacheline_aligned_in_smp = { |
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.lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED, |
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}; |
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u64 notrace trace_clock_global(void) { unsigned long flags; int this_cpu; u64 now; |
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local_irq_save(flags); |
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this_cpu = raw_smp_processor_id(); now = cpu_clock(this_cpu); /* * If in an NMI context then dont risk lockups and return the * cpu_clock() time: */ if (unlikely(in_nmi())) goto out; |
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arch_spin_lock(&trace_clock_struct.lock); |
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/* * TODO: if this happens often then maybe we should reset |
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* my_scd->clock to prev_time+1, to make sure |
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* we start ticking with the local clock from now on? */ |
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if ((s64)(now - trace_clock_struct.prev_time) < 0) now = trace_clock_struct.prev_time + 1; |
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trace_clock_struct.prev_time = now; |
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arch_spin_unlock(&trace_clock_struct.lock); |
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out: |
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local_irq_restore(flags); |
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return now; } |
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static atomic64_t trace_counter; /* * trace_clock_counter(): simply an atomic counter. * Use the trace_counter "counter" for cases where you do not care * about timings, but are interested in strict ordering. */ u64 notrace trace_clock_counter(void) { return atomic64_add_return(1, &trace_counter); } |