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

From	Thomas Gleixner <tglx@linutronix.de>
Newsgroups	linux.kernel
Subject	Re: [patch V2 00/20] timer: Refactor the timer wheel
Date	2016-06-17 16:00 +0200
Message-ID	<rL2tr-7fP-13@gated-at.bofh.it> (permalink)
References	<rL20p-73O-3@gated-at.bofh.it> <rL2jL-7aI-7@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Fri, 17 Jun 2016, Eric Dumazet wrote:
> >
> >    To achieve this capacity with HZ=1000 without increasing the storage size
> >    by another level, we reduced the granularity of the first wheel level from
> >    1ms to 4ms. According to our data, there is no user which relies on that
> >    1ms granularity and 99% of those timers are canceled before expiry.
> >
> 
> Ah... This might be a problem for people using small TCP RTO timers in
> datacenters (order of 5 ms)
> (and small delay ack timers as well, in the order of 4 ms)
> 
> TCP/pacing uses high resolution timer in sch_fq.c so no problem there.
> 
> If we arm a timer for 5 ms, what are the exact consequences ?

The worst case expiry time is 8ms on HZ=1000 as it is on HZ=250

> I fear we might trigger lot more of spurious retransmits.
> 
> Or maybe I should read the patch series. I'll take some time today.

Maybe just throw it at such a workload and see what happens :)

Thanks,

	tglx

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
  [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

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