tracing: implement trace_clock_*() APIs
Impact: implement new tracing timestamp APIs Add three 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 Make the ring-buffer use the local trace clock internally. Acked-by: Peter Zijlstra <peterz@infradead.org> Acked-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Ingo Molnar <mingo@elte.hu>
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4 changed files with 123 additions and 3 deletions
19
include/linux/trace_clock.h
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19
include/linux/trace_clock.h
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@ -0,0 +1,19 @@
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#ifndef _LINUX_TRACE_CLOCK_H
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#define _LINUX_TRACE_CLOCK_H
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/*
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* 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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#include <linux/compiler.h>
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#include <linux/types.h>
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extern u64 notrace trace_clock_local(void);
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extern u64 notrace trace_clock(void);
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extern u64 notrace trace_clock_global(void);
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#endif /* _LINUX_TRACE_CLOCK_H */
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@ -19,6 +19,7 @@ obj-$(CONFIG_FUNCTION_TRACER) += libftrace.o
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obj-$(CONFIG_RING_BUFFER) += ring_buffer.o
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obj-$(CONFIG_TRACING) += trace.o
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obj-$(CONFIG_TRACING) += trace_clock.o
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obj-$(CONFIG_TRACING) += trace_output.o
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obj-$(CONFIG_TRACING) += trace_stat.o
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obj-$(CONFIG_CONTEXT_SWITCH_TRACER) += trace_sched_switch.o
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@ -4,6 +4,7 @@
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* Copyright (C) 2008 Steven Rostedt <srostedt@redhat.com>
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*/
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#include <linux/ring_buffer.h>
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#include <linux/trace_clock.h>
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#include <linux/ftrace_irq.h>
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#include <linux/spinlock.h>
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#include <linux/debugfs.h>
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@ -12,7 +13,6 @@
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#include <linux/module.h>
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#include <linux/percpu.h>
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#include <linux/mutex.h>
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#include <linux/sched.h> /* used for sched_clock() (for now) */
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#include <linux/init.h>
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#include <linux/hash.h>
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#include <linux/list.h>
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@ -112,14 +112,13 @@ EXPORT_SYMBOL_GPL(tracing_is_on);
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/* Up this if you want to test the TIME_EXTENTS and normalization */
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#define DEBUG_SHIFT 0
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/* FIXME!!! */
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u64 ring_buffer_time_stamp(int cpu)
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{
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u64 time;
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preempt_disable_notrace();
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/* shift to debug/test normalization and TIME_EXTENTS */
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time = sched_clock() << DEBUG_SHIFT;
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time = trace_clock_local() << DEBUG_SHIFT;
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preempt_enable_no_resched_notrace();
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return time;
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101
kernel/trace/trace_clock.c
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101
kernel/trace/trace_clock.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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