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From: Thomas Gleixner <tglx@linutronix.de>
To: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
	LKML <linux-kernel@vger.kernel.org>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	Eric Dumazet <edumazet@google.com>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	Chris Mason <clm@fb.com>, Arjan van de Ven <arjan@infradead.org>,
	rt@linutronix.de, Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [patch 13/20] timer: Switch to a non cascading wheel
Date: Tue, 14 Jun 2016 18:28:43 +0200 (CEST)	[thread overview]
Message-ID: <alpine.DEB.2.11.1606141213300.5839@nanos> (raw)
In-Reply-To: <20160614101144.GA849@gmail.com>

On Tue, 14 Jun 2016, Ingo Molnar wrote:
> * Thomas Gleixner <tglx@linutronix.de> wrote:
> > On Mon, 13 Jun 2016, Peter Zijlstra wrote:
> > > On Mon, Jun 13, 2016 at 08:41:00AM -0000, Thomas Gleixner wrote:
> > > > +
> > > > +	/* Cascading, sigh... */
> > > 
> > > So given that userspace has no influence on timer period; can't we
> > > simply fail to support timers longer than 30 minutes?
> > > 
> > > In anything really arming timers _that_ long?
> > 
> > Unfortunately yes. Networking being one of those. Real cascading happens once
> > in a blue moon, but it happens.
> 
> So I'd really prefer it if we added a few more levels, a hard limit and got rid of 
> the cascading once and for all!
> 
> IMHO 'once in a blue moon' code is much worse than a bit more data overhead.

I agree. If we add two wheel levels then we end up with:

  HZ 1000:  134217727 ms ~=  37 hours
  HZ  250:  536870908 ms ~= 149 hours
  HZ  100: 1342177270 ms ~= 372 hours 

Looking through all my data I found exactly one timeout which is insanely
large: 120 hours!

That's net/netfilter/nf_conntrack_core.c:
      setup_timer(&ct->timeout, death_by_timeout, (unsigned long)ct);

Anything else is way below 37 hours.

Thanks,

	tglx

  reply	other threads:[~2016-06-14 16:30 UTC|newest]

Thread overview: 62+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-06-13  8:40 [patch 00/20] timer: Refactor the timer wheel Thomas Gleixner
2016-06-13  8:40 ` [patch 01/20] timer: Make pinned a timer property Thomas Gleixner
2016-06-13  8:40 ` [patch 02/20] x86/apic/uv: Initialize timer as pinned Thomas Gleixner
2016-06-13  8:40 ` [patch 03/20] x86/mce: " Thomas Gleixner
2016-06-13  8:40 ` [patch 04/20] cpufreq/powernv: " Thomas Gleixner
2016-06-13 13:18   ` Arjan van de Ven
2016-06-13  8:40 ` [patch 05/20] driver/net/ethernet/tile: " Thomas Gleixner
2016-06-13  8:40 ` [patch 06/20] drivers/tty/metag_da: " Thomas Gleixner
2016-06-13 13:13   ` Arjan van de Ven
2016-06-13  8:40 ` [patch 07/20] drivers/tty/mips_ejtag: " Thomas Gleixner
2016-06-13  8:40 ` [patch 08/20] net/ipv4/inet: Initialize timers " Thomas Gleixner
2016-06-13  8:40 ` [patch 09/20] timer: Remove mod_timer_pinned Thomas Gleixner
2016-06-13  8:40 ` [patch 10/20] timer: Add a cascading tracepoint Thomas Gleixner
2016-06-13  8:40 ` [patch 11/20] hlist: Add hlist_is_last_node() helper Thomas Gleixner
2016-06-13 10:27   ` Paolo Bonzini
2016-06-13  8:40 ` [patch 12/20] timer: Give a few structs and members proper names Thomas Gleixner
2016-06-13  8:41 ` [patch 13/20] timer: Switch to a non cascading wheel Thomas Gleixner
2016-06-13 11:40   ` Peter Zijlstra
2016-06-13 12:30     ` Thomas Gleixner
2016-06-13 12:46       ` Eric Dumazet
2016-06-13 14:30         ` Thomas Gleixner
2016-06-14 10:11       ` Ingo Molnar
2016-06-14 16:28         ` Thomas Gleixner [this message]
2016-06-14 17:14           ` Arjan van de Ven
2016-06-14 18:05             ` Thomas Gleixner
2016-06-14 20:34               ` Peter Zijlstra
2016-06-14 20:42               ` Peter Zijlstra
2016-06-14 21:17                 ` Eric Dumazet
2016-06-15 14:53                   ` Thomas Gleixner
2016-06-15 14:55                     ` Arjan van de Ven
2016-06-15 16:43                       ` Thomas Gleixner
2016-06-16 15:43                         ` Thomas Gleixner
2016-06-16 16:02                           ` Paul E. McKenney
2016-06-16 18:14                             ` Peter Zijlstra
2016-06-17  0:40                               ` Paul E. McKenney
2016-06-17  4:04                                 ` Paul E. McKenney
2016-06-16 16:04                           ` Arjan van de Ven
2016-06-16 16:09                             ` Thomas Gleixner
2016-06-15 15:05                     ` Eric Dumazet
2016-06-13 14:36   ` Richard Cochran
2016-06-13 14:39     ` Thomas Gleixner
2016-06-13  8:41 ` [patch 15/20] timer: Move __run_timers() function Thomas Gleixner
2016-06-13  8:41 ` [patch 14/20] timer: Remove slack leftovers Thomas Gleixner
2016-06-13  8:41 ` [patch 16/20] timer: Optimize collect timers for NOHZ Thomas Gleixner
2016-06-13  8:41 ` [patch 17/20] tick/sched: Remove pointless empty function Thomas Gleixner
2016-06-13  8:41 ` [patch 18/20] timer: Forward wheel clock whenever possible Thomas Gleixner
2016-06-13 15:14   ` Richard Cochran
2016-06-13 15:18     ` Thomas Gleixner
2016-06-13  8:41 ` [patch 19/20] timer: Split out index calculation Thomas Gleixner
2016-06-13  8:41 ` [patch 20/20] timer: Optimization for same expiry time in mod_timer() Thomas Gleixner
2016-06-13 14:10 ` [patch 00/20] timer: Refactor the timer wheel Eric Dumazet
2016-06-13 16:15 ` Paul E. McKenney
2016-06-15 15:15   ` Paul E. McKenney
2016-06-15 17:02     ` Thomas Gleixner
2016-06-15 20:26       ` Paul E. McKenney
2016-06-14  8:16 [patch 13/20] timer: Switch to a non cascading wheel George Spelvin
2016-06-14  8:50 ` Thomas Gleixner
2016-06-14 10:15   ` George Spelvin
2016-06-14 10:20 ` Peter Zijlstra
2016-06-14 12:58   ` George Spelvin
2016-06-14 16:48     ` Thomas Gleixner
2016-06-14 19:56       ` George Spelvin

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