Re: [RFC PATCH 1/3] Unified trace buffer

[Ingo Molnar <mingo@elte.hu>]

* Ingo Molnar <mingo@elte.hu> wrote:

> * Linus Torvalds <torvalds@linux-foundation.org> wrote:
> 
> > On Thu, 25 Sep 2008, Linus Torvalds wrote:
> > > 
> > > You also ignore the early trace issues, and have apparently not used 
> > > it for FTRACE. You also ignore the fact that without TSC, it goes 
> > > into the same "crap mode" that is appropriate for the scheduler, but 
> > > totally useless for tracing.
> > 
> > Oh, and I didn't notice (because Steven pointed out "notrace" and I 
> > didn't see any of them), that in order to get things to work you had 
> > just added
> > 
> > CFLAGS_REMOVE_lockdep.o = -pg
> > CFLAGS_REMOVE_lockdep_proc.o = -pg
> > CFLAGS_REMOVE_mutex-debug.o = -pg
> > CFLAGS_REMOVE_rtmutex-debug.o = -pg
> > CFLAGS_REMOVE_cgroup-debug.o = -pg
> > CFLAGS_REMOVE_sched_clock.o = -pg
> > CFLAGS_REMOVE_sched.o = -mno-spe -pg
> > 
> > all ovr the place, which was part of my argument against this crap in 
> > the first place.
> 
> Really, we traced all these files for ages. I can restore it if it's 
> worthwile - but lockdep totally kills the usability of function 
> traces, it inserts thousands of uninteresting events over and over 
> again.

to prove it, i just applied this patch:

Index: linux/kernel/Makefile
===================================================================
--- linux.orig/kernel/Makefile
+++ linux/kernel/Makefile
@@ -21,7 +21,6 @@ CFLAGS_REMOVE_mutex-debug.o = -pg
 CFLAGS_REMOVE_rtmutex-debug.o = -pg
 CFLAGS_REMOVE_cgroup-debug.o = -pg
 CFLAGS_REMOVE_sched_clock.o = -pg
-CFLAGS_REMOVE_sched.o = -mno-spe -pg
 endif
 
 obj-$(CONFIG_PROFILING) += profile.o

and sched.o was fully traced again. For example schedule() to idle is 38 
function calls:

$ cd /debug/tracing
$ echo ftrace > current_tracer
$ cat trace

# tracer: ftrace
#
#           TASK-PID    CPU#    TIMESTAMP  FUNCTION
#              | |       |          |         |
[...]
             ssh-2734  [001]    52.291772: schedule <-schedule_timeout
             ssh-2734  [001]    52.291772: hrtick_clear <-schedule
             ssh-2734  [001]    52.291774: _spin_lock <-schedule
             ssh-2734  [001]    52.291775: deactivate_task <-schedule
             ssh-2734  [001]    52.291776: dequeue_task <-deactivate_task
             ssh-2734  [001]    52.291777: dequeue_task_fair <-dequeue_task
             ssh-2734  [001]    52.291778: update_curr <-dequeue_task_fair
             ssh-2734  [001]    52.291779: calc_delta_mine <-update_curr
             ssh-2734  [001]    52.291780: hrtick_start_fair <-dequeue_task_fair
             ssh-2734  [001]    52.291782: find_busiest_group <-schedule
             ssh-2734  [001]    52.291783: idle_cpu <-find_busiest_group
             ssh-2734  [001]    52.291784: target_load <-find_busiest_group
             ssh-2734  [001]    52.291785: weighted_cpuload <-target_load
             ssh-2734  [001]    52.291786: weighted_cpuload <-find_busiest_group
             ssh-2734  [001]    52.291787: cpu_avg_load_per_task <-find_busiest_group
             ssh-2734  [001]    52.291788: source_load <-find_busiest_group
             ssh-2734  [001]    52.291789: weighted_cpuload <-source_load
             ssh-2734  [001]    52.291790: weighted_cpuload <-find_busiest_group
             ssh-2734  [001]    52.291791: cpu_avg_load_per_task <-find_busiest_group
             ssh-2734  [001]    52.291792: msecs_to_jiffies <-schedule
             ssh-2734  [001]    52.291792: msecs_to_jiffies <-schedule
             ssh-2734  [001]    52.291793: put_prev_task_fair <-schedule
             ssh-2734  [001]    52.291795: pick_next_task_fair <-schedule
             ssh-2734  [001]    52.291796: pick_next_task_rt <-schedule
             ssh-2734  [001]    52.291796: pick_next_task_fair <-schedule
             ssh-2734  [001]    52.291797: pick_next_task_idle <-schedule
             ssh-2734  [001]    52.291798: _spin_trylock <-tracing_record_cmdline
             ssh-2734  [001]    52.291800: _spin_unlock <-tracing_record_cmdline
             ssh-2734  [001]    52.291802: __switch_to <-thread_return
          <idle>-0     [001]    52.291804: finish_task_switch <-thread_return
          <idle>-0     [001]    52.291805: _spin_unlock_irq <-finish_task_switch
          <idle>-0     [001]    52.291806: tick_nohz_stop_sched_tick <-cpu_idle
          <idle>-0     [001]    52.291807: ktime_get <-tick_nohz_stop_sched_tick
          <idle>-0     [001]    52.291807: ktime_get_ts <-ktime_get
          <idle>-0     [001]    52.291808: getnstimeofday <-ktime_get_ts
          <idle>-0     [001]    52.291808: acpi_pm_read <-getnstimeofday
          <idle>-0     [001]    52.291810: set_normalized_timespec <-ktime_get_ts
          <idle>-0     [001]    52.291811: get_next_timer_interrupt <-tick_nohz_stop_sched_tick

it worked just fine in my first blind attempt.

	Ingo