/* * 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> #include <linux/hardirq.h> #include <linux/module.h> #include <linux/percpu.h> #include <linux/sched.h> #include <linux/ktime.h> #include <linux/trace_clock.h> /* * 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) { unsigned long flags; u64 clock; /* * sched_clock() is an architecture implemented, fast, scalable, * lockless clock. It is not guaranteed to be coherent across * CPUs, nor across CPU idle events. */ raw_local_irq_save(flags); clock = sched_clock(); raw_local_irq_restore(flags); return clock; } /* * trace_clock(): 'inbetween' trace clock. Not completely serialized, * 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) { return cpu_clock(raw_smp_processor_id()); } /* * 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. */ static u64 prev_trace_clock_time; static raw_spinlock_t trace_clock_lock ____cacheline_aligned_in_smp = (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED; u64 notrace trace_clock_global(void) { unsigned long flags; int this_cpu; u64 now; raw_local_irq_save(flags); 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; __raw_spin_lock(&trace_clock_lock); /* * TODO: if this happens often then maybe we should reset * my_scd->clock to prev_trace_clock_time+1, to make sure * we start ticking with the local clock from now on? */ if ((s64)(now - prev_trace_clock_time) < 0) now = prev_trace_clock_time + 1; prev_trace_clock_time = now; __raw_spin_unlock(&trace_clock_lock); out: raw_local_irq_restore(flags); return now; }