Re: [LTP] [patch V2 00/20] timer: Refactor the timer wheel

From	"George Spelvin" <linux@sciencehorizons.net>
Newsgroups	linux.kernel
Subject	Re: [LTP] [patch V2 00/20] timer: Refactor the timer wheel
Date	2016-06-23 16:00 +0200
Message-ID	<rNdkK-2nl-23@gated-at.bofh.it> (permalink)
References	<rNbsB-12A-17@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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Cyril Hrubis wrote:
> Thomas Gleixner wrote:
>> Err. You know that the timer expired because sigtimedwait() returns
>> EAGAIN. And the only thing you can reliably check for is that the timer did
>> not expired to early. Anything else is guesswork and voodoo programming.

> But seriously is there a reason
> why OS that is not under heavy load cannot expire timers with reasonable
> overruns? I.e. if I ask for a second of sleep and expect it to be woken
> up not much more than half of a second later?

> If we stick only to guarantees that are defined in POSIX playing music
> with mplayer would not be possible since it sleeps in futex() and if it
> wakes too late it will fail to fill buffers. In practice this worked
> fine for me for years.

Two points:
1) sigtimedwait() is unusual in that it uses the jiffies timer.  Most
   system call timeouts (including specifically the one in FUTEX_WAIT)
   use the high-resolution timer subsystem, which is a whole different
   animal with tighter guarantees, and
2) The worst-case error in tglx's proposal is 1/8 of the requested
   timeout: the wakeup is after 112.5% of the requested time, plus
   one tick.  This is well within your requested accuracy.  (For very
   short timeouts, the "plus one tick" can dominate the percentage error.)

Thread

[patch V2 00/20] timer: Refactor the timer wheel Thomas Gleixner <tglx@linutronix.de> - 2016-06-17 15:30 +0200
  [patch V2 20/20] timer: Optimization for same expiry time in  mod_timer() Thomas Gleixner <tglx@linutronix.de> - 2016-06-17 15:30 +0200
  [patch V2 11/20] timer: Give a few structs and members proper names Thomas Gleixner <tglx@linutronix.de> - 2016-06-17 15:30 +0200
  [patch V2 15/20] timer: Optimize collect timers for NOHZ Thomas Gleixner <tglx@linutronix.de> - 2016-06-17 15:30 +0200
  [patch V2 19/20] timer: Split out index calculation Thomas Gleixner <tglx@linutronix.de> - 2016-06-17 15:30 +0200
  [patch V2 06/20] drivers/tty/metag_da: Initialize timer as pinned Thomas Gleixner <tglx@linutronix.de> - 2016-06-17 15:40 +0200
  [patch V2 01/20] timer: Make pinned a timer property Thomas Gleixner <tglx@linutronix.de> - 2016-06-17 15:40 +0200
  [patch V2 10/20] hlist: Add hlist_is_singular_node() helper Thomas Gleixner <tglx@linutronix.de> - 2016-06-17 15:40 +0200
  [patch V2 04/20] cpufreq/powernv: Initialize timer as pinned Thomas Gleixner <tglx@linutronix.de> - 2016-06-17 15:40 +0200
  [patch V2 08/20] net/ipv4/inet: Initialize timers as pinned Thomas Gleixner <tglx@linutronix.de> - 2016-06-17 15:40 +0200
  [patch V2 03/20] x86/mce: Initialize timer as pinned Thomas Gleixner <tglx@linutronix.de> - 2016-06-17 15:40 +0200
  [patch V2 17/20] timer: Forward wheel clock whenever possible Thomas Gleixner <tglx@linutronix.de> - 2016-06-17 15:40 +0200
  [patch V2 02/20] x86/apic/uv: Initialize timer as pinned Thomas Gleixner <tglx@linutronix.de> - 2016-06-17 15:40 +0200
  [patch V2 14/20] timer: Move __run_timers() function Thomas Gleixner <tglx@linutronix.de> - 2016-06-17 15:40 +0200
  [patch V2 12/20] timer: Switch to a non cascading wheel Thomas Gleixner <tglx@linutronix.de> - 2016-06-17 15:40 +0200
    Re: [patch V2 12/20] timer: Switch to a non cascading wheel "George Spelvin" <linux@sciencehorizons.net> - 2016-06-18 12:00 +0200
      Re: [patch V2 12/20] timer: Switch to a non cascading wheel Thomas Gleixner <tglx@linutronix.de> - 2016-06-24 12:10 +0200
  [patch V2 09/20] timer: Remove mod_timer_pinned Thomas Gleixner <tglx@linutronix.de> - 2016-06-17 15:40 +0200
  [patch V2 13/20] timer: Remove slack leftovers Thomas Gleixner <tglx@linutronix.de> - 2016-06-17 15:40 +0200
  [patch V2 05/20] driver/net/ethernet/tile: Initialize timer as pinned Thomas Gleixner <tglx@linutronix.de> - 2016-06-17 15:40 +0200
    Re: [patch V2 05/20] driver/net/ethernet/tile: Initialize timer as  pinned Peter Zijlstra <peterz@infradead.org> - 2016-06-21 20:50 +0200
  [patch V2 18/20] timer: Only wake softirq if necessary Thomas Gleixner <tglx@linutronix.de> - 2016-06-17 15:40 +0200
  Re: [patch V2 00/20] timer: Refactor the timer wheel Eric Dumazet <edumazet@google.com> - 2016-06-17 15:50 +0200
    Re: [patch V2 00/20] timer: Refactor the timer wheel Thomas Gleixner <tglx@linutronix.de> - 2016-06-17 16:00 +0200
      Re: [patch V2 00/20] timer: Refactor the timer wheel Eric Dumazet <edumazet@google.com> - 2016-06-17 16:30 +0200
        Re: [patch V2 00/20] timer: Refactor the timer wheel Thomas Gleixner <tglx@linutronix.de> - 2016-06-20 16:00 +0200
          Re: [patch V2 00/20] timer: Refactor the timer wheel Thomas Gleixner <tglx@linutronix.de> - 2016-06-20 16:50 +0200
            Re: [patch V2 00/20] timer: Refactor the timer wheel Arjan van de Ven <arjanvandeven@gmail.com> - 2016-06-20 18:10 +0200
          Re: [patch V2 00/20] timer: Refactor the timer wheel Arjan van de Ven <arjanvandeven@gmail.com> - 2016-06-20 16:50 +0200
          Re: [patch V2 00/20] timer: Refactor the timer wheel Rik van Riel <riel@redhat.com> - 2016-06-20 21:10 +0200
            Re: [patch V2 00/20] timer: Refactor the timer wheel Eric Dumazet <edumazet@google.com> - 2016-06-21 04:50 +0200
  Re: [patch V2 00/20] timer: Refactor the timer wheel Arjan van de Ven <arjanvandeven@gmail.com> - 2016-06-17 16:30 +0200
  Re: [patch V2 00/20] timer: Refactor the timer wheel Thomas Gleixner <tglx@linutronix.de> - 2016-06-20 17:20 +0200
    Re: [patch V2 00/20] timer: Refactor the timer wheel "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-06-20 17:50 +0200
  Re: [patch V2 00/20] timer: Refactor the timer wheel "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-06-20 17:40 +0200
  Re: [patch V2 00/20] timer: Refactor the timer wheel Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-06-22 09:40 +0200
    Re: [patch V2 00/20] timer: Refactor the timer wheel Thomas Gleixner <tglx@linutronix.de> - 2016-06-22 10:50 +0200
      Re: [patch V2 00/20] timer: Refactor the timer wheel Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-06-22 11:10 +0200
        Re: [patch V2 00/20] timer: Refactor the timer wheel Mike Galbraith <umgwanakikbuti@gmail.com> - 2016-06-22 15:40 +0200
      Re: [LTP] [patch V2 00/20] timer: Refactor the timer wheel Cyril Hrubis <chrubis@suse.cz> - 2016-06-22 12:40 +0200
        Re: [LTP] [patch V2 00/20] timer: Refactor the timer wheel Thomas Gleixner <tglx@linutronix.de> - 2016-06-23 10:30 +0200
          Re: [LTP] [patch V2 00/20] timer: Refactor the timer wheel Cyril Hrubis <chrubis@suse.cz> - 2016-06-23 14:00 +0200
            Re: [LTP] [patch V2 00/20] timer: Refactor the timer wheel "George Spelvin" <linux@sciencehorizons.net> - 2016-06-23 16:00 +0200
              Re: [LTP] [patch V2 00/20] timer: Refactor the timer wheel Thomas Gleixner <tglx@linutronix.de> - 2016-06-23 16:20 +0200
              Re: [LTP] [patch V2 00/20] timer: Refactor the timer wheel Cyril Hrubis <chrubis@suse.cz> - 2016-06-23 17:20 +0200
                Re: [LTP] [patch V2 00/20] timer: Refactor the timer wheel Thomas Gleixner <tglx@linutronix.de> - 2016-06-23 17:30 +0200
                Re: [LTP] [patch V2 00/20] timer: Refactor the timer wheel Cyril Hrubis <chrubis@suse.cz> - 2016-06-23 18:40 +0200
      Re: [patch V2 00/20] timer: Refactor the timer wheel Pavel Machek <pavel@ucw.cz> - 2016-06-26 21:10 +0200
        Re: [patch V2 00/20] timer: Refactor the timer wheel Arjan van de Ven <arjanvandeven@gmail.com> - 2016-06-26 21:30 +0200
          Re: [patch V2 00/20] timer: Refactor the timer wheel Pavel Machek <pavel@ucw.cz> - 2016-06-26 22:10 +0200

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