no## This is a template for a generic "war story" (systemtap sample usage) writeup.

Kernel Profiling


One might wonder what the kernel is up to in general, but requring only a general overview with rough sampling, where the overhead is minimal. The following script gives one an impression.



global profile, pcount
probe timer.profile {
  pcount <<< 1
  fn = user_mode() ? "<user>" : symname(addr())
  if (fn != "") profile[fn] <<< 1
probe {
  printf ("\n--- %d samples recorded:\n", @count(pcount))
  foreach (f in profile- limit 10) {
    printf ("%s\t%d\n", f, @count(profile[f]))
  delete profile
  delete pcount


# stap pf2.stp
--- 109 samples recorded:
mwait_idle      71
check_poison_obj        4
_spin_unlock_irqrestore 2
dbg_redzone1    1
kfree   1
kmem_cache_free 1
_spin_unlock_irq        1
end_buffer_write_sync   1
lock_acquire    1
--- 108 samples recorded:
mwait_idle      91
check_poison_obj        3
_spin_unlock_irq        2
delay_tsc       1


This script samples using the timer interrupt, which occurs perhaps tens to hundreds of times a second. Since the timer.profile handler uses aggregate globals, it can run concurrently on a multiprocessor machine.

User-space functions are excluded from the profile, so what will tend to show up are kernel-intensive workloads, or idleness ("mwait_idle" on recent kernels). Programs that are simply busy in user space will not show up with this script.

See also WSFunctionCallCount.

None: WSKernelProfile (last edited 2011-12-09 15:40:01 by MarkWielaard)