tracing: implement trace_clock_*() APIs (14131f2f) · Commits · e / devices / android_kernel_teracube_emerald

include/linux/trace_clock.h

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		#ifndef _LINUX_TRACE_CLOCK_H
		#define _LINUX_TRACE_CLOCK_H

		/*
		* 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
		*/
		#include <linux/compiler.h>
		#include <linux/types.h>

		extern u64 notrace trace_clock_local(void);
		extern u64 notrace trace_clock(void);
		extern u64 notrace trace_clock_global(void);

		#endif /* _LINUX_TRACE_CLOCK_H */

kernel/trace/Makefile

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		@@ -19,6 +19,7 @@ obj-$(CONFIG_FUNCTION_TRACER) += libftrace.o
		obj-$(CONFIG_RING_BUFFER) += ring_buffer.o

		obj-$(CONFIG_TRACING) += trace.o
		obj-$(CONFIG_TRACING) += trace_clock.o
		obj-$(CONFIG_TRACING) += trace_output.o
		obj-$(CONFIG_TRACING) += trace_stat.o
		obj-$(CONFIG_CONTEXT_SWITCH_TRACER) += trace_sched_switch.o

kernel/trace/ring_buffer.c

+2 −3

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		@@ -4,6 +4,7 @@
		* Copyright (C) 2008 Steven Rostedt <srostedt@redhat.com>
		*/
		#include <linux/ring_buffer.h>
		#include <linux/trace_clock.h>
		#include <linux/ftrace_irq.h>
		#include <linux/spinlock.h>
		#include <linux/debugfs.h>
		@@ -12,7 +13,6 @@
		#include <linux/module.h>
		#include <linux/percpu.h>
		#include <linux/mutex.h>
		#include <linux/sched.h> /* used for sched_clock() (for now) */
		#include <linux/init.h>
		#include <linux/hash.h>
		#include <linux/list.h>
		@@ -112,14 +112,13 @@ EXPORT_SYMBOL_GPL(tracing_is_on);
		/* Up this if you want to test the TIME_EXTENTS and normalization */
		#define DEBUG_SHIFT 0

		/* FIXME!!! */
		u64 ring_buffer_time_stamp(int cpu)
		{
		u64 time;

		preempt_disable_notrace();
		/* shift to debug/test normalization and TIME_EXTENTS */
		time = sched_clock() << DEBUG_SHIFT;
		time = trace_clock_local() << DEBUG_SHIFT;
		preempt_enable_no_resched_notrace();

		return time;

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>
		#include <linux/hardirq.h>
		#include <linux/module.h>
		#include <linux/percpu.h>
		#include <linux/sched.h>
		#include <linux/ktime.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)
		{
		/*
		* sched_clock() is an architecture implemented, fast, scalable,
		* lockless clock. It is not guaranteed to be coherent across
		* CPUs, nor across CPU idle events.
		*/
		return sched_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;
		}