ftrace - The kernel function tracer - 1

1. Introduction

• Ftrace is a tracing utility built directly into the Linux kernel.
• Designed to help out developers and designers of systems to find what is going on inside the kernel.
• Below mentioned output is executed in ubuntu 12.04 virtual machine.

2. Build kernel with the following configuration(Ubuntu already Configured)

CONFIG_FUNCTION_GRAPH_TRACER
CONFIG_STACK_TRACER
CONFIG_DYNAMIC_FTRACE
CONFIG_FUNCTION_TRACER

3. Mount the debugfs

#mount -t debugfs nodev /sys/kernel/debug

#mount |grep debugfs
5:none on /sys/kernel/debug type debugfs (rw)

4. Enter in to root shell

$ sudo  -i 

You will be asked for your password, then be given a root shell. In that shell, you can cd to /sys/kernel/debug.

5. Sample Execution

# pwd
/sys/kernel/debug/tracing

# cat available_tracers 
blk function_graph mmiotrace wakeup_rt wakeup function nop

# echo function_graph > current_tracer

# cat current_tracer 
function_graph

# cat trace | head -20
# tracer: function_graph
#
# CPU  DURATION                  FUNCTION CALLS
# |     |   |                     |   |   |   |
 0) ! 164785.8 us |      } /* native_safe_halt */
 0) ! 164786.9 us |    } /* default_idle.part.4 */
 0) ! 164787.6 us |  } /* default_idle */
 0)   0.062 us    |  local_touch_nmi();
 0)               |  cpuidle_idle_call() {
 0)   0.094 us    |    cpuidle_get_driver();
 0)   0.690 us    |  }
 0)               |  default_idle() {
 0)               |    default_idle.part.4() {
 0)               |      native_safe_halt() {
 0)   ==========> |
 0)               |        do_IRQ() {
 0)               |          irq_enter() {
 0)               |            rcu_irq_enter() {
 0)   0.231 us    |              rcu_exit_nohz();
 0)   0.995 us    |            }

Continue reading more from Part 2.

http://linuxseekernel.blogspot.com/2014/05/ftrace-kernel-function-tracer-2.html

6. References

1. http://lwn.net/Articles/365835/
2. https://www.kernel.org/doc/Documentation/trace/ftrace.txt