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
......@@ -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.
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
/*
* 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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