linux-kernel - Re: [patch 13/20] timer: Switch to a non cascading wheel

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Date:	Tue, 14 Jun 2016 20:05:49 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Arjan van de Ven <arjanvandeven@...il.com>
cc:	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Chris Mason <clm@...com>,
	Arjan van de Ven <arjan@...radead.org>, rt@...utronix.de,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [patch 13/20] timer: Switch to a non cascading wheel

On Tue, 14 Jun 2016, Arjan van de Ven wrote:

> evaluating a 120 hours timer ever 37 hours to see if it should fire...
> not too horrid.

Well that thing is doing weird stuff anyway:

   swapper     0 [001] 1789995.305532: timer:timer_start: timer=0xffff8800c8346920 function=death_by_timeout expires=4850639994 [timeout=108000000]
             ssh  3870 [001] 1790025.284704: timer:timer_cancel: timer=0xffff8800c8346920
             ssh  3870 [001] 1790025.284707: timer:timer_start: timer=0xffff8800c8346920 function=death_by_timeout expires=4742722493 [timeout=75000]
         swapper     0 [001] 1790025.330514: timer:timer_cancel: timer=0xffff8800c8346920
         swapper     0 [001] 1790025.330515: timer:timer_start: timer=0xffff8800c8346920 function=death_by_timeout expires=4850647504 [timeout=108000000]
             ssh  3870 [001] 1790055.307058: timer:timer_cancel: timer=0xffff8800c8346920
             ssh  3870 [001] 1790055.307060: timer:timer_start: timer=0xffff8800c8346920 function=death_by_timeout expires=4742730003 [timeout=75000]
         swapper     0 [001] 1790055.352146: timer:timer_cancel: timer=0xffff8800c8346920

And that goes on forever. 2834 such sequences for this particular timer
instance in 4.5 hours. 90000 sequences total for all timers related to
death_by_timeout in 4.5 hours

No idea what this is doing and why the heck it nees a 120 hour timeout ....

Thanks,

	tglx