Re: [patch V2 08/10] timer: Implement the hierarchical pull model

From	Thomas Gleixner <tglx@linutronix.de>
Newsgroups	linux.kernel
Subject	Re: [patch V2 08/10] timer: Implement the hierarchical pull model
Date	2017-04-19 11:50 +0200
Message-ID	<txUpk-1NP-7@gated-at.bofh.it> (permalink)
References	<txEue-8r4-5@gated-at.bofh.it> <txEuf-8r4-41@gated-at.bofh.it> <txTMC-1zl-31@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Wed, 19 Apr 2017, Peter Zijlstra wrote:
> > +done:
> > +	raw_spin_unlock(&group->lock);
> > +	return nextevt;
> > +}
> 
> Would it be very onerous to rewrite that into regular loops? That avoids
> us having to think (and worry) about blowing our stack.

The issue is that this is walking a hierarchy tree (limited depth) and not
a list of groups at a particular level.

In an earlier version we checked the stack usage and it was ~128 bytes per
nest level. With 32k CPUs this ends up with maximum 5 recursions, i.e. 640
bytes. I recheck with the current implementation.

Thanks,

	tglx

Thread

[patch V2 00/10] timer: Move from a push remote at enqueue to a pull  at expiry model Thomas Gleixner <tglx@linutronix.de> - 2017-04-18 18:50 +0200
  [patch V2 06/10] timer: Restructure internal locking Thomas Gleixner <tglx@linutronix.de> - 2017-04-18 18:50 +0200
    Re: [patch V2 06/10] timer: Restructure internal locking Peter Zijlstra <peterz@infradead.org> - 2017-04-19 09:10 +0200
  [patch V2 10/10] timer: Always queue timers on the local CPU Thomas Gleixner <tglx@linutronix.de> - 2017-04-18 18:50 +0200
  [patch V2 07/10] tick/sched: Split out jiffies update helper function Thomas Gleixner <tglx@linutronix.de> - 2017-04-18 18:50 +0200
  [patch V2 08/10] timer: Implement the hierarchical pull model Thomas Gleixner <tglx@linutronix.de> - 2017-04-18 18:50 +0200
    Re: [patch V2 08/10] timer: Implement the hierarchical pull model Peter Zijlstra <peterz@infradead.org> - 2017-04-19 09:30 +0200
    Re: [patch V2 08/10] timer: Implement the hierarchical pull model Peter Zijlstra <peterz@infradead.org> - 2017-04-19 09:30 +0200
    Re: [patch V2 08/10] timer: Implement the hierarchical pull model Peter Zijlstra <peterz@infradead.org> - 2017-04-19 09:40 +0200
    Re: [patch V2 08/10] timer: Implement the hierarchical pull model Peter Zijlstra <peterz@infradead.org> - 2017-04-19 09:40 +0200
    Re: [patch V2 08/10] timer: Implement the hierarchical pull model Peter Zijlstra <peterz@infradead.org> - 2017-04-19 10:20 +0200
      Re: [patch V2 08/10] timer: Implement the hierarchical pull model Peter Zijlstra <peterz@infradead.org> - 2017-04-19 10:40 +0200
        Re: [patch V2 08/10] timer: Implement the hierarchical pull model Thomas Gleixner <tglx@linutronix.de> - 2017-04-19 11:10 +0200
      Re: [patch V2 08/10] timer: Implement the hierarchical pull model Thomas Gleixner <tglx@linutronix.de> - 2017-04-19 10:40 +0200
    Re: [patch V2 08/10] timer: Implement the hierarchical pull model Peter Zijlstra <peterz@infradead.org> - 2017-04-19 11:00 +0200
    Re: [patch V2 08/10] timer: Implement the hierarchical pull model Peter Zijlstra <peterz@infradead.org> - 2017-04-19 11:10 +0200
      Re: [patch V2 08/10] timer: Implement the hierarchical pull model Peter Zijlstra <peterz@infradead.org> - 2017-04-19 11:50 +0200
        Re: [patch V2 08/10] timer: Implement the hierarchical pull model Peter Zijlstra <peterz@infradead.org> - 2017-04-19 12:00 +0200
      Re: [patch V2 08/10] timer: Implement the hierarchical pull model Thomas Gleixner <tglx@linutronix.de> - 2017-04-19 11:50 +0200
        Re: [patch V2 08/10] timer: Implement the hierarchical pull model Peter Zijlstra <peterz@infradead.org> - 2017-04-19 12:00 +0200
    Re: [patch V2 08/10] timer: Implement the hierarchical pull model Peter Zijlstra <peterz@infradead.org> - 2017-04-19 11:30 +0200
    Re: [patch V2 08/10] timer: Implement the hierarchical pull model Peter Zijlstra <peterz@infradead.org> - 2017-04-19 12:30 +0200
  [patch V2 05/10] timer: Retrieve next expiry of pinned/non-pinned  timers seperately Thomas Gleixner <tglx@linutronix.de> - 2017-04-18 18:50 +0200
    Re: [patch V2 05/10] timer: Retrieve next expiry of  pinned/non-pinned timers seperately Peter Zijlstra <peterz@infradead.org> - 2017-04-19 09:10 +0200
      Re: [patch V2 05/10] timer: Retrieve next expiry of pinned/non-pinned  timers seperately Thomas Gleixner <tglx@linutronix.de> - 2017-04-19 12:00 +0200
  [patch V2 04/10] timer: Keep the pinned timers separate from the  others Thomas Gleixner <tglx@linutronix.de> - 2017-04-18 18:50 +0200
  Re: [patch V2 00/10] timer: Move from a push remote at enqueue to a  pull at expiry model "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-04-21 21:30 +0200

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