Re: Use case for TASKS_RCU

From	Steven Rostedt <rostedt@goodmis.org>
Newsgroups	linux.kernel
Subject	Re: Use case for TASKS_RCU
Date	2017-05-19 16:30 +0200
Message-ID	<tIR4J-3uF-15@gated-at.bofh.it> (permalink)
References	(1 earlier) <tHE9A-22D-21@gated-at.bofh.it> <tHJLZ-5yL-35@gated-at.bofh.it> <tIJAd-6Ek-11@gated-at.bofh.it> <tIQim-2MD-21@gated-at.bofh.it> <tIQLo-3eE-15@gated-at.bofh.it>
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On Fri, 19 May 2017 10:04:21 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> On Fri, 19 May 2017 06:35:50 -0700
> "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote:
> 
> > Simpler would be better!
> > 
> > However, is it really guaranteed that one SCHED_IDLE thread cannot
> > preempt another?  If not, then the trampoline-freeing SCHED_IDLE thread
> > might preempt some other SCHED_IDLE thread in the middle of a trampoline.
> > I am not seeing anything that prevents such preemption, but it is rather
> > early local time, so I could easily be missing something.
> > 
> > However, if SCHED_IDLE threads cannot preempt other threads, even other
> > SCHED_IDLE threads, then your approach sounds quite promising to me.
> > 
> > Steve, Peter, thoughts?  
> 
> SCHED_IDLE is the swapper task. There's one on each CPU, and they don't
> migrate. And they only get called when there's no other task running.

Peter just "schooled" me on IRC. I stand corrected (and he may respond
to this email too). I guess any task can become SCHED_IDLE.

But that just makes this an even less likely option for
synchronize_rcu_tasks().

-- Steve

Thread

Use case for TASKS_RCU "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-05-15 20:30 +0200
  Re: Use case for TASKS_RCU Steven Rostedt <rostedt@goodmis.org> - 2017-05-15 20:50 +0200
    Re: Use case for TASKS_RCU "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-05-15 22:20 +0200
  Re: Use case for TASKS_RCU Ingo Molnar <mingo@kernel.org> - 2017-05-16 08:30 +0200
    Re: Use case for TASKS_RCU "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-05-16 14:30 +0200
      Re: Use case for TASKS_RCU Steven Rostedt <rostedt@goodmis.org> - 2017-05-16 15:10 +0200
        Re: Use case for TASKS_RCU Masami Hiramatsu <mhiramat@kernel.org> - 2017-05-24 11:40 +0200
      Re: Use case for TASKS_RCU Ingo Molnar <mingo@kernel.org> - 2017-05-19 08:30 +0200
        Re: Use case for TASKS_RCU "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-05-19 15:40 +0200
          Re: Use case for TASKS_RCU Steven Rostedt <rostedt@goodmis.org> - 2017-05-19 16:10 +0200
            Re: Use case for TASKS_RCU Steven Rostedt <rostedt@goodmis.org> - 2017-05-19 16:30 +0200
              Re: Use case for TASKS_RCU "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-05-19 21:10 +0200
                Re: Use case for TASKS_RCU "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-05-23 02:10 +0200
                Re: Use case for TASKS_RCU Steven Rostedt <rostedt@goodmis.org> - 2017-05-23 07:30 +0200
                Re: Use case for TASKS_RCU "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-05-23 17:40 +0200
                Re: Use case for TASKS_RCU Steven Rostedt <rostedt@goodmis.org> - 2017-05-23 21:50 +0200
                Re: Use case for TASKS_RCU "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-05-23 22:10 +0200
                Re: Use case for TASKS_RCU Steven Rostedt <rostedt@goodmis.org> - 2017-05-23 22:50 +0200
                Re: Use case for TASKS_RCU "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-05-23 23:20 +0200

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