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Re: [PATCH 0/5 v2] tracing: Add usecase of synchronize_rcu_tasks() and stack_tracer_disable()

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On Fri, 7 Apr 2017 07:43:35 -0700
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote:

> On Fri, Apr 07, 2017 at 10:01:06AM -0400, Steven Rostedt wrote:
> > Paul,
> > 
> > Here's my latest. You OK with it?  
> 
> Given your update to 3/5, I suspect that we could live with it.  I am
> expecting some complaints about increases in idle-entry latency, but might
> be best to wait for complaints rather than complexifying too proactively.

We only added a this_cpu_inc() and this_cpu_dec() which are very fast
operations. I highly doubt it will be measurable. Although, I'm talking
about x86, IIRC, the this_cpu_inc/dec were be poorly written for other
archs in the past. I'm not sure if that was fixed though.

> 
> That said, there isn't supposed to be any tracing during the now very
> small interval where RCU's idle-entry is incomplete.  Mightn't it be
> better to (under CONFIG_PROVE_RCU or some such) give splats if tracing
> showed up in that interval?
> 

Again, tracing is not the issue. I do function tracing in that location
without any problems. The issue here was the stack tracer.

Maybe we can create a new variable that is more cache local to the RCU
code.

What about calling it "rcu_disabled"? Then tracing that depends on RCU
can simply check that.

s/stack_trace_disable/disable_rcu/
s/stack_trace_enable/enable_rcu/

export a per cpu variable rcu_disabled

Then I can have the stack tracer check that variable as well. And we
could even put in a WARN_ON(this_cpu_read(rcu_disabled) in the
TRACE_EVENT() macros.

Thoughts?

-- Steve

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[PATCH 0/5 v2] tracing: Add usecase of synchronize_rcu_tasks() and stack_tracer_disable() Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 16:10 +0200
  [PATCH 1/5 v2] ftrace: Add use of synchronize_rcu_tasks() with dynamic trampolines Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 16:10 +0200
  [PATCH 3/5 v2] tracing: Add stack_tracer_disable/enable() functions Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 16:10 +0200
    [PATCH 3/5 v2.1] tracing: Add stack_tracer_disable/enable()  functions Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 16:30 +0200
    Re: [PATCH 3/5 v2] tracing: Add stack_tracer_disable/enable()  functions Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 16:30 +0200
  Re: [PATCH 0/5 v2] tracing: Add usecase of synchronize_rcu_tasks()  and stack_tracer_disable() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-04-07 16:50 +0200
    Re: [PATCH 0/5 v2] tracing: Add usecase of synchronize_rcu_tasks()  and stack_tracer_disable() Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 17:10 +0200
      Re: [PATCH 0/5 v2] tracing: Add usecase of synchronize_rcu_tasks()  and stack_tracer_disable() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-04-07 17:20 +0200
        Re: [PATCH 0/5 v2] tracing: Add usecase of synchronize_rcu_tasks()  and stack_tracer_disable() Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 17:30 +0200
  [PATCH 6/5]rcu/tracing: Add rcu_disabled to denote when  rcu_irq_enter() will not work Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 18:40 +0200
    Re: [PATCH 6/5]rcu/tracing: Add rcu_disabled to denote when  rcu_irq_enter() will not work "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-04-07 18:50 +0200
      Re: [PATCH 6/5]rcu/tracing: Add rcu_disabled to denote when  rcu_irq_enter() will not work Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 18:50 +0200
        Re: [PATCH 6/5]rcu/tracing: Add rcu_disabled to denote when  rcu_irq_enter() will not work "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-04-07 19:00 +0200
      [PATCH 6/5 v2] rcu/tracing: Add rcu_disabled to denote when  rcu_irq_enter() will not work Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 19:10 +0200
        Re: [PATCH 6/5 v2] rcu/tracing: Add rcu_disabled to denote when  rcu_irq_enter() will not work "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-04-07 19:20 +0200
  [PATCH 7/5] tracing: Make sure rcu_irq_enter() can work for  trace_*_rcuidle() trace events Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 19:10 +0200
    Re: [PATCH 7/5] tracing: Make sure rcu_irq_enter() can work for  trace_*_rcuidle() trace events "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-04-07 19:20 +0200
    Re: [PATCH 7/5] tracing: Make sure rcu_irq_enter() can work for  trace_*_rcuidle() trace events Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2017-04-07 19:20 +0200
      Re: [PATCH 7/5] tracing: Make sure rcu_irq_enter() can work for  trace_*_rcuidle() trace events Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 19:30 +0200
        Re: [PATCH 7/5] tracing: Make sure rcu_irq_enter() can work for  trace_*_rcuidle() trace events Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 19:40 +0200
        Re: [PATCH 7/5] tracing: Make sure rcu_irq_enter() can work for  trace_*_rcuidle() trace events Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2017-04-07 19:50 +0200
          Re: [PATCH 7/5] tracing: Make sure rcu_irq_enter() can work for  trace_*_rcuidle() trace events Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 20:00 +0200
          [PATCH 7/5 v3] tracing: Make sure rcu_irq_enter() can work for  trace_*_rcuidle() trace events Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 20:20 +0200
            Re: [PATCH 7/5 v3] tracing: Make sure rcu_irq_enter() can work for  trace_*_rcuidle() trace events Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2017-04-07 20:20 +0200
              Re: [PATCH 7/5 v4] tracing: Make sure rcu_irq_enter() can work for  trace_*_rcuidle() trace events Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 21:50 +0200
              [PATCH 7/5 v4] tracing: Make sure rcu_irq_enter() can work for  trace_*_rcuidle() trace events Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 21:50 +0200
      Re: [PATCH 7/5] tracing: Make sure rcu_irq_enter() can work for  trace_*_rcuidle() trace events Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 19:30 +0200
      [PATCH 7/5 v2] tracing: Make sure rcu_irq_enter() can work for  trace_*_rcuidle() trace events Steven Rostedt <rostedt@goodmis.org> - 2017-04-07 19:50 +0200

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