linux-kernel - Re: [PATCH 00/18] tracing/ring-buffer: fixes for latency tracer [2.6.32]

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Date:	Tue, 8 Sep 2009 16:42:50 +0200
From:	Jan Blunck <jblunck@...e.de>
To:	Arnaldo Carvalho de Melo <acme@...hat.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>,
	Clark Williams <williams@...hat.com>,
	linux-rt-users@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH 00/18] tracing/ring-buffer: fixes for latency tracer 
	[2.6.32]

On Mon, Sep 7, 2009 at 12:20 PM, Jan Blunck<jblunck@...e.de> wrote:
> On Sat, Sep 5, 2009 at 5:06 PM, Arnaldo Carvalho de Melo<acme@...hat.com> wrote:
>>
>> I did a quick port to tip/rt/head and couldn't reproduce the problems I
>> was experiencing, thanks!
>>
>> I've put the ported patch series at:
>>
>> http://userweb.kernel.org/~acme/rostedt-rb-rt
>>

Besides the problem with the wakeup tracer I see traces with
preemptirqsoff that I think are invalid:

# tracer: preemptirqsoff
#
# preemptirqsoff latency trace v1.1.5 on 2.6.31-rc8-rt9-rt_trace
# --------------------------------------------------------------------
# latency: 332 us, #4/4, CPU#24 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:32)
#    -----------------
#    | task: -0 (uid:0 nice:0 policy:0 rt_prio:0)
#    -----------------
#  => started at: start_secondary
#  => ended at:   start_secondary
#
#
#                  _------=> CPU#
#                 / _-----=> irqs-off
#                | / _----=> need-resched
#                || / _---=> hardirq/softirq
#                ||| / _--=> preempt-depth
#                |||| /
#                |||||     delay
#  cmd     pid   ||||| time  |   caller
#     \   /      |||||   \   |   /
  <idle>-0      24.N.1    0us : cpu_idle <-start_secondary
  <idle>-0      24dN.1    1us!: tick_nohz_stop_idle <-tick_nohz_restart_sched_ti
ck
  <idle>-0      24dN.1  332us+: cpu_idle <-start_secondary
  <idle>-0      24dN.1  336us : trace_preempt_on <-start_secondary

I have set kernel.ftrace_enabled = 1 but still not a single function
is recorded in tick_nohz_stop_idle().

Any ideas?
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