Re: RCU stall when using function_graph

From	Daniel Lezcano <daniel.lezcano@linaro.org>
Newsgroups	linux.kernel
Subject	Re: RCU stall when using function_graph
Date	2017-08-03 16:40 +0200
Message-ID	<uaps5-1gd-7@gated-at.bofh.it> (permalink)
References	(2 earlier) <u9Pyh-2wR-3@gated-at.bofh.it> <ua1g6-1vG-7@gated-at.bofh.it> <ua1zs-1Rq-19@gated-at.bofh.it> <uamNA-7Pj-11@gated-at.bofh.it> <uanJF-8s6-29@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Thu, Aug 03, 2017 at 05:44:21AM -0700, Paul E. McKenney wrote:

[ ... ]

> > > BTW, function_graph tracer is the most invasive of the tracers. It's 4x
> > > slower than function tracer. I'm wondering if the tracer isn't the
> > > cause, but just slows things down enough to cause a some other race
> > > condition that triggers the bug.
> > 
> > Yes, that could be true.
> > 
> > I tried the following scenario:
> > 
> >  - cpufreq governor => userspace + max_freq (1.2GHz)
> >    - function_graph set ==> OK
> > 
> >  - cpufreq governor => userspace + min_freq (200MHz)
> >    - function_graph set ==> RCU stall
> > 
> > Beside that, I realize the board is constantly processing SOF interrupts
> > every 124us, so that adds more overhead.
> > 
> > Removing the USB support, thus the associated processing for the SOF
> > interrupts, I don't see anymore the RCU stall.
> 
> Looks like Steve called this one!  ;-)

Yep :)

> > Is it the expected behavior to have the system hang after a RCU stall
> > raises ?
> 
> No, but if NMI stack traces are enabled and there are any NMI problems,
> bad things can happen.  In addition, the bulk of output can cause problems
> if you have a slow console connection.

Ok, thanks.

  -- Daniel

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Thread

Re: RCU stall when using function_graph "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-08-02 00:10 +0200
  Re: RCU stall when using function_graph Daniel Lezcano <daniel.lezcano@linaro.org> - 2017-08-02 00:20 +0200
    Re: RCU stall when using function_graph Steven Rostedt <rostedt@goodmis.org> - 2017-08-02 02:20 +0200
      Re: RCU stall when using function_graph Daniel Lezcano <daniel.lezcano@linaro.org> - 2017-08-02 14:50 +0200
        Re: RCU stall when using function_graph Steven Rostedt <rostedt@goodmis.org> - 2017-08-02 15:10 +0200
          Re: RCU stall when using function_graph "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-08-03 04:50 +0200
          Re: RCU stall when using function_graph Daniel Lezcano <daniel.lezcano@linaro.org> - 2017-08-03 13:50 +0200
            Re: RCU stall when using function_graph "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-08-03 14:50 +0200
              Re: RCU stall when using function_graph Daniel Lezcano <daniel.lezcano@linaro.org> - 2017-08-03 16:40 +0200
                Re: RCU stall when using function_graph "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-08-06 19:10 +0200
                Re: RCU stall when using function_graph Pratyush Anand <panand@redhat.com> - 2017-08-09 11:20 +0200
                Re: RCU stall when using function_graph "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-08-09 15:00 +0200
                Re: RCU stall when using function_graph Daniel Lezcano <daniel.lezcano@linaro.org> - 2017-08-09 15:30 +0200
                Re: RCU stall when using function_graph "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-08-09 16:50 +0200
                Re: RCU stall when using function_graph Daniel Lezcano <daniel.lezcano@linaro.org> - 2017-08-09 18:00 +0200
                Re: RCU stall when using function_graph "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-08-09 19:30 +0200
                Re: RCU stall when using function_graph Daniel Lezcano <daniel.lezcano@linaro.org> - 2017-08-10 11:50 +0200
                Re: RCU stall when using function_graph "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-08-10 23:40 +0200
                Re: RCU stall when using function_graph Daniel Lezcano <daniel.lezcano@linaro.org> - 2017-08-11 11:40 +0200
        Re: RCU stall when using function_graph "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-08-02 19:00 +0200
  Re: RCU stall when using function_graph "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-08-02 14:50 +0200

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