1 /* 2 * tracing clocks 3 * 4 * Copyright (C) 2009 Red Hat, Inc., Ingo Molnar <mingo@redhat.com> 5 * 6 * Implements 3 trace clock variants, with differing scalability/precision 7 * tradeoffs: 8 * 9 * - local: CPU-local trace clock 10 * - medium: scalable global clock with some jitter 11 * - global: globally monotonic, serialized clock 12 * 13 * Tracer plugins will chose a default from these clocks. 14 */ 15 #include <linux/spinlock.h> 16 #include <linux/irqflags.h> 17 #include <linux/hardirq.h> 18 #include <linux/module.h> 19 #include <linux/percpu.h> 20 #include <linux/sched.h> 21 #include <linux/sched/clock.h> 22 #include <linux/ktime.h> 23 #include <linux/trace_clock.h> 24 25 /* 26 * trace_clock_local(): the simplest and least coherent tracing clock. 27 * 28 * Useful for tracing that does not cross to other CPUs nor 29 * does it go through idle events. 30 */ 31 u64 notrace trace_clock_local(void) 32 { 33 u64 clock; 34 35 /* 36 * sched_clock() is an architecture implemented, fast, scalable, 37 * lockless clock. It is not guaranteed to be coherent across 38 * CPUs, nor across CPU idle events. 39 */ 40 preempt_disable_notrace(); 41 clock = sched_clock(); 42 preempt_enable_notrace(); 43 44 return clock; 45 } 46 EXPORT_SYMBOL_GPL(trace_clock_local); 47 48 /* 49 * trace_clock(): 'between' trace clock. Not completely serialized, 50 * but not completely incorrect when crossing CPUs either. 51 * 52 * This is based on cpu_clock(), which will allow at most ~1 jiffy of 53 * jitter between CPUs. So it's a pretty scalable clock, but there 54 * can be offsets in the trace data. 55 */ 56 u64 notrace trace_clock(void) 57 { 58 return local_clock(); 59 } 60 EXPORT_SYMBOL_GPL(trace_clock); 61 62 /* 63 * trace_jiffy_clock(): Simply use jiffies as a clock counter. 64 * Note that this use of jiffies_64 is not completely safe on 65 * 32-bit systems. But the window is tiny, and the effect if 66 * we are affected is that we will have an obviously bogus 67 * timestamp on a trace event - i.e. not life threatening. 68 */ 69 u64 notrace trace_clock_jiffies(void) 70 { 71 return jiffies_64_to_clock_t(jiffies_64 - INITIAL_JIFFIES); 72 } 73 EXPORT_SYMBOL_GPL(trace_clock_jiffies); 74 75 /* 76 * trace_clock_global(): special globally coherent trace clock 77 * 78 * It has higher overhead than the other trace clocks but is still 79 * an order of magnitude faster than GTOD derived hardware clocks. 80 * 81 * Used by plugins that need globally coherent timestamps. 82 */ 83 84 /* keep prev_time and lock in the same cacheline. */ 85 static struct { 86 u64 prev_time; 87 arch_spinlock_t lock; 88 } trace_clock_struct ____cacheline_aligned_in_smp = 89 { 90 .lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED, 91 }; 92 93 u64 notrace trace_clock_global(void) 94 { 95 unsigned long flags; 96 int this_cpu; 97 u64 now; 98 99 raw_local_irq_save(flags); 100 101 this_cpu = raw_smp_processor_id(); 102 now = sched_clock_cpu(this_cpu); 103 /* 104 * If in an NMI context then dont risk lockups and return the 105 * cpu_clock() time: 106 */ 107 if (unlikely(in_nmi())) 108 goto out; 109 110 arch_spin_lock(&trace_clock_struct.lock); 111 112 /* 113 * TODO: if this happens often then maybe we should reset 114 * my_scd->clock to prev_time+1, to make sure 115 * we start ticking with the local clock from now on? 116 */ 117 if ((s64)(now - trace_clock_struct.prev_time) < 0) 118 now = trace_clock_struct.prev_time + 1; 119 120 trace_clock_struct.prev_time = now; 121 122 arch_spin_unlock(&trace_clock_struct.lock); 123 124 out: 125 raw_local_irq_restore(flags); 126 127 return now; 128 } 129 EXPORT_SYMBOL_GPL(trace_clock_global); 130 131 static atomic64_t trace_counter; 132 133 /* 134 * trace_clock_counter(): simply an atomic counter. 135 * Use the trace_counter "counter" for cases where you do not care 136 * about timings, but are interested in strict ordering. 137 */ 138 u64 notrace trace_clock_counter(void) 139 { 140 return atomic64_add_return(1, &trace_counter); 141 } 142