Re: [patch 00/20] timer: Refactor the timer wheel

From	Thomas Gleixner <tglx@linutronix.de>
Newsgroups	linux.kernel
Subject	Re: [patch 00/20] timer: Refactor the timer wheel
Date	2016-06-15 19:10 +0200
Message-ID	<rKmud-5m4-9@gated-at.bofh.it> (permalink)
References	<rJvJf-3OU-5@gated-at.bofh.it> <rJCKK-eX-17@gated-at.bofh.it> <rKkLL-4en-5@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Wed, 15 Jun 2016, Paul E. McKenney wrote:
> On Mon, Jun 13, 2016 at 09:15:14AM -0700, Paul E. McKenney wrote:
> > On Mon, Jun 13, 2016 at 08:40:50AM -0000, Thomas Gleixner wrote:
> > > The current timer wheel has some drawbacks:
> > > 
> > > 1) Cascading
> > > 
> > >    Cascading can be an unbound operation and is completely pointless in most
> > >    cases because the vast majority of the timer wheel timers are canceled or
> > >    rearmed before expiration.
> > > 
> > > 2) No fast lookup of the next expiring timer
> > > 
> > >    In NOHZ scenarios the first timer soft interrupt after a long NOHZ period
> > >    must fast forward the base time to current jiffies. As we have no way to
> > >    find the next expiring timer fast, the code loops and increments the base
> > >    time by one and checks for expired timers in each step. I've observed loops
> > >    lasting 1 ms!
> > > 
> > > There are some other issues caused by the above, but they are minor compare to
> > > those.
> > 
> > For SMP configurations, this passes light rcutorture testing.  For UP
> > builds, it complains about undefined symbols.  Builds succeed with
> > the following kneejerk patch.  Am retesting rcutorture.
> 
> And with the patch below, testing goes as well with your patch stack as
> it does without it.  So, with that patch (or equivalent):
> 
> Tested-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> 
> There were some complaints about increasing the size of the tiny
> configuration, FYI.

I know. The extra storage space for the deferrable stuff makes it larger along
with the extra code for avoiding all the crap which the current wheel suffers
from :) Do the tiny people need NOHZ?

> So, just out of curiosity, does anyone still run -rt on single-CPU systems?

Of course :)

Thanks,

	tglx

Thread

[patch 00/20] timer: Refactor the timer wheel Thomas Gleixner <tglx@linutronix.de> - 2016-06-13 10:50 +0200
  [patch 11/20] hlist: Add hlist_is_last_node() helper Thomas Gleixner <tglx@linutronix.de> - 2016-06-13 10:50 +0200
    Re: [patch 11/20] hlist: Add hlist_is_last_node() helper Paolo Bonzini <pbonzini@redhat.com> - 2016-06-13 12:30 +0200
  [patch 07/20] drivers/tty/mips_ejtag: Initialize timer as pinned Thomas Gleixner <tglx@linutronix.de> - 2016-06-13 10:50 +0200
  [patch 01/20] timer: Make pinned a timer property Thomas Gleixner <tglx@linutronix.de> - 2016-06-13 10:50 +0200
  [patch 17/20] tick/sched: Remove pointless empty function Thomas Gleixner <tglx@linutronix.de> - 2016-06-13 10:50 +0200
  [patch 05/20] driver/net/ethernet/tile: Initialize timer as pinned Thomas Gleixner <tglx@linutronix.de> - 2016-06-13 10:50 +0200
  [patch 15/20] timer: Move __run_timers() function Thomas Gleixner <tglx@linutronix.de> - 2016-06-13 10:50 +0200
  [patch 12/20] timer: Give a few structs and members proper names Thomas Gleixner <tglx@linutronix.de> - 2016-06-13 10:50 +0200
  [patch 04/20] cpufreq/powernv: Initialize timer as pinned Thomas Gleixner <tglx@linutronix.de> - 2016-06-13 10:50 +0200
    Re: [patch 04/20] cpufreq/powernv: Initialize timer as pinned Arjan van de Ven <arjanvandeven@gmail.com> - 2016-06-13 15:20 +0200
  [patch 13/20] timer: Switch to a non cascading wheel Thomas Gleixner <tglx@linutronix.de> - 2016-06-13 10:50 +0200
    Re: [patch 13/20] timer: Switch to a non cascading wheel Peter Zijlstra <peterz@infradead.org> - 2016-06-13 13:50 +0200
      Re: [patch 13/20] timer: Switch to a non cascading wheel Thomas Gleixner <tglx@linutronix.de> - 2016-06-13 14:40 +0200
        Re: [patch 13/20] timer: Switch to a non cascading wheel Eric Dumazet <edumazet@google.com> - 2016-06-13 14:50 +0200
          Re: [patch 13/20] timer: Switch to a non cascading wheel Thomas Gleixner <tglx@linutronix.de> - 2016-06-13 16:40 +0200
        Re: [patch 13/20] timer: Switch to a non cascading wheel Ingo Molnar <mingo@kernel.org> - 2016-06-14 12:20 +0200
          Re: [patch 13/20] timer: Switch to a non cascading wheel Thomas Gleixner <tglx@linutronix.de> - 2016-06-14 18:40 +0200
            Re: [patch 13/20] timer: Switch to a non cascading wheel Arjan van de Ven <arjanvandeven@gmail.com> - 2016-06-14 19:20 +0200
              Re: [patch 13/20] timer: Switch to a non cascading wheel Thomas Gleixner <tglx@linutronix.de> - 2016-06-14 20:10 +0200
                Re: [patch 13/20] timer: Switch to a non cascading wheel Peter Zijlstra <peterz@infradead.org> - 2016-06-14 22:40 +0200
                Re: [patch 13/20] timer: Switch to a non cascading wheel Peter Zijlstra <peterz@infradead.org> - 2016-06-14 22:50 +0200
                Re: [patch 13/20] timer: Switch to a non cascading wheel Eric Dumazet <edumazet@google.com> - 2016-06-14 23:20 +0200
                Re: [patch 13/20] timer: Switch to a non cascading wheel Thomas Gleixner <tglx@linutronix.de> - 2016-06-15 17:00 +0200
                Re: [patch 13/20] timer: Switch to a non cascading wheel Arjan van de Ven <arjanvandeven@gmail.com> - 2016-06-15 17:00 +0200
                Re: [patch 13/20] timer: Switch to a non cascading wheel Thomas Gleixner <tglx@linutronix.de> - 2016-06-15 18:50 +0200
                Re: [patch 13/20] timer: Switch to a non cascading wheel Thomas Gleixner <tglx@linutronix.de> - 2016-06-16 17:50 +0200
                Re: [patch 13/20] timer: Switch to a non cascading wheel "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-06-16 18:10 +0200
                Re: [patch 13/20] timer: Switch to a non cascading wheel Peter Zijlstra <peterz@infradead.org> - 2016-06-16 20:20 +0200
                Re: [patch 13/20] timer: Switch to a non cascading wheel "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-06-17 02:50 +0200
                Re: [patch 13/20] timer: Switch to a non cascading wheel "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-06-17 06:10 +0200
                Re: [patch 13/20] timer: Switch to a non cascading wheel Arjan van de Ven <arjanvandeven@gmail.com> - 2016-06-16 18:10 +0200
                Re: [patch 13/20] timer: Switch to a non cascading wheel Thomas Gleixner <tglx@linutronix.de> - 2016-06-16 18:20 +0200
                Re: [patch 13/20] timer: Switch to a non cascading wheel Eric Dumazet <edumazet@google.com> - 2016-06-15 17:10 +0200
    Re: [patch 13/20] timer: Switch to a non cascading wheel Richard Cochran <richardcochran@gmail.com> - 2016-06-13 16:40 +0200
      Re: [patch 13/20] timer: Switch to a non cascading wheel Thomas Gleixner <tglx@linutronix.de> - 2016-06-13 16:50 +0200
  [patch 14/20] timer: Remove slack leftovers Thomas Gleixner <tglx@linutronix.de> - 2016-06-13 10:50 +0200
  [patch 18/20] timer: Forward wheel clock whenever possible Thomas Gleixner <tglx@linutronix.de> - 2016-06-13 10:50 +0200
    Re: [patch 18/20] timer: Forward wheel clock whenever possible Richard Cochran <richardcochran@gmail.com> - 2016-06-13 17:20 +0200
      Re: [patch 18/20] timer: Forward wheel clock whenever possible Thomas Gleixner <tglx@linutronix.de> - 2016-06-13 17:30 +0200
  [patch 06/20] drivers/tty/metag_da: Initialize timer as pinned Thomas Gleixner <tglx@linutronix.de> - 2016-06-13 11:00 +0200
    Re: [patch 06/20] drivers/tty/metag_da: Initialize timer as pinned Arjan van de Ven <arjanvandeven@gmail.com> - 2016-06-13 15:20 +0200
  [patch 03/20] x86/mce: Initialize timer as pinned Thomas Gleixner <tglx@linutronix.de> - 2016-06-13 11:00 +0200
  [patch 08/20] net/ipv4/inet: Initialize timers as pinned Thomas Gleixner <tglx@linutronix.de> - 2016-06-13 11:00 +0200
  [patch 02/20] x86/apic/uv: Initialize timer as pinned Thomas Gleixner <tglx@linutronix.de> - 2016-06-13 11:00 +0200
  Re: [patch 00/20] timer: Refactor the timer wheel Eric Dumazet <edumazet@google.com> - 2016-06-13 16:20 +0200
  Re: [patch 00/20] timer: Refactor the timer wheel "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-06-13 18:20 +0200
    Re: [patch 00/20] timer: Refactor the timer wheel "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-06-15 17:20 +0200
      Re: [patch 00/20] timer: Refactor the timer wheel Thomas Gleixner <tglx@linutronix.de> - 2016-06-15 19:10 +0200
        Re: [patch 00/20] timer: Refactor the timer wheel "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-06-15 22:30 +0200

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