Commit 35e8e302 authored by Steven Rostedt's avatar Steven Rostedt Committed by Thomas Gleixner
Browse files

ftrace: add tracing of context switches 



This patch adds context switch tracing, of the format of:

                  _------=> CPU#
                 / _-----=> irqs-off
                | / _----=> need-resched
                || / _---=> hardirq/softirq
                ||| / _--=> preempt-depth
                |||| /
                |||||     delay
    cmd     pid ||||| time  |      pid:prio:state
       \   /    |||||   \   |      /
  swapper-0     1d..3    137us+:  0:140:R --> 2912:120
     sshd-2912  1d..3    216us+:  2912:120:S --> 0:140
  swapper-0     1d..3    261us+:  0:140:R --> 2912:120
     bash-2920  0d..3    267us+:  2920:120:S --> 0:140
     sshd-2912  1d..3    330us!:  2912:120:S --> 0:140
  swapper-0     1d..3   2389us+:  0:140:R --> 2847:120
 yum-upda-2847  1d..3   2411us!:  2847:120:S --> 0:140
  swapper-0     0d..3  11089us+:  0:140:R --> 3139:120
 gdm-bina-3139  0d..3  11113us!:  3139:120:S --> 0:140
  swapper-0     1d..3 102328us+:  0:140:R --> 2847:120
 yum-upda-2847  1d..3 102348us!:  2847:120:S --> 0:140

 "sched_switch" is added to /debugfs/tracing/available_tracers

[ Eugene Teo <eugeneteo@kernel.sg: remove unused tracing_sched_switch_enabled ]

Signed-off-by: default avatarSteven Rostedt <srostedt@redhat.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent 1b29b018

kernel/trace/Kconfig

+11 −0
Original line number Diff line number Diff line
@@ -13,6 +13,7 @@ config FTRACE 
	depends on DEBUG_KERNEL && HAVE_FTRACE

	select FRAME_POINTER

	select TRACING

	select CONTEXT_SWITCH_TRACER

	help

	  Enable the kernel to trace every kernel function. This is done

	  by using a compiler feature to insert a small, 5-byte No-Operation
@@ -21,3 +22,13 @@ config FTRACE 
	  tracing is enabled by the administrator. If it's runtime disabled

	  (the bootup default), then the overhead of the instructions is very

	  small and not measurable even in micro-benchmarks.



config CONTEXT_SWITCH_TRACER

	bool "Trace process context switches"

	depends on DEBUG_KERNEL

	select TRACING

	select MARKERS

	help

	  This tracer gets called from the context switch and records

	  all switching of tasks.

kernel/trace/Makefile

+1 −0
Original line number Diff line number Diff line 
obj-$(CONFIG_FTRACE) += libftrace.o



obj-$(CONFIG_TRACING) += trace.o

obj-$(CONFIG_CONTEXT_SWITCH_TRACER) += trace_sched_switch.o

obj-$(CONFIG_FTRACE) += trace_functions.o



libftrace-y := ftrace.o

kernel/trace/trace_sched_switch.c

0 → 100644
+116 −0
Original line number Diff line number Diff line 
/*

 * trace context switch

 *

 * Copyright (C) 2007 Steven Rostedt <srostedt@redhat.com>

 *

 */

#include <linux/module.h>

#include <linux/fs.h>

#include <linux/debugfs.h>

#include <linux/kallsyms.h>

#include <linux/uaccess.h>

#include <linux/marker.h>

#include <linux/ftrace.h>



#include "trace.h"



static struct trace_array	*ctx_trace;

static int __read_mostly	tracer_enabled;



static void notrace

ctx_switch_func(struct task_struct *prev, struct task_struct *next)

{

	struct trace_array *tr = ctx_trace;

	struct trace_array_cpu *data;

	unsigned long flags;

	long disabled;

	int cpu;



	if (!tracer_enabled)

		return;



	raw_local_irq_save(flags);

	cpu = raw_smp_processor_id();

	data = tr->data[cpu];

	disabled = atomic_inc_return(&data->disabled);



	if (likely(disabled == 1))

		tracing_sched_switch_trace(tr, data, prev, next, flags);



	atomic_dec(&data->disabled);

	raw_local_irq_restore(flags);

}



void ftrace_ctx_switch(struct task_struct *prev, struct task_struct *next)

{

	tracing_record_cmdline(prev);



	/*

	 * If tracer_switch_func only points to the local

	 * switch func, it still needs the ptr passed to it.

	 */

	ctx_switch_func(prev, next);



	/*

	 * Chain to the wakeup tracer (this is a NOP if disabled):

	 */

	wakeup_sched_switch(prev, next);

}



static notrace void sched_switch_reset(struct trace_array *tr)

{

	int cpu;



	tr->time_start = now(tr->cpu);



	for_each_online_cpu(cpu)

		tracing_reset(tr->data[cpu]);

}



static notrace void start_sched_trace(struct trace_array *tr)

{

	sched_switch_reset(tr);

	tracer_enabled = 1;

}



static notrace void stop_sched_trace(struct trace_array *tr)

{

	tracer_enabled = 0;

}



static notrace void sched_switch_trace_init(struct trace_array *tr)

{

	ctx_trace = tr;



	if (tr->ctrl)

		start_sched_trace(tr);

}



static notrace void sched_switch_trace_reset(struct trace_array *tr)

{

	if (tr->ctrl)

		stop_sched_trace(tr);

}



static void sched_switch_trace_ctrl_update(struct trace_array *tr)

{

	/* When starting a new trace, reset the buffers */

	if (tr->ctrl)

		start_sched_trace(tr);

	else

		stop_sched_trace(tr);

}



static struct tracer sched_switch_trace __read_mostly =

{

	.name		= "sched_switch",

	.init		= sched_switch_trace_init,

	.reset		= sched_switch_trace_reset,

	.ctrl_update	= sched_switch_trace_ctrl_update,

};



__init static int init_sched_switch_trace(void)

{

	return register_tracer(&sched_switch_trace);

}

device_initcall(init_sched_switch_trace);

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