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: Steven Rostedt <srostedt@redhat.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 11 insertions, 0 deletions

diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 1399f372b5dc..5d6aa92866cd 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -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.
+