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

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Date:	Mon, 20 Jun 2016 19:48:12 -0700
From:	Eric Dumazet <edumazet@...gle.com>
To:	Rik van Riel <riel@...hat.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.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>,
	George Spelvin <linux@...encehorizons.net>,
	Len Brown <lenb@...nel.org>
Subject: Re: [patch V2 00/20] timer: Refactor the timer wheel

On Mon, Jun 20, 2016 at 12:03 PM, Rik van Riel <riel@...hat.com> wrote:
> On Mon, 2016-06-20 at 15:56 +0200, Thomas Gleixner wrote:
>>
>> 2) Cut off at 37hrs for HZ=1000. We could make this configurable as a
>> 1000HZ
>>    option so datacenter folks can use this and people who don't care
>> and want
>>    better batching for power can use the 4ms thingy.
>>
>
> It might be easy enough to simply re-queue a timer that
> has not expired yet after 37 hours.
>
> How many 37 hour timers will there be outstanding at any
> one time, that expire around the same time?
>
> Chances are, not many at all. In fact, the vast majority
> of them are likely to be deleted long before they ever
> expire.
>
> Timers lasting longer than 37 hours do not seem like
> something worth optimizing for.
>

I totally agree that these long timers should probably be handled (if
really someone needs them)
using an additional set of helpers able to rearm the timer if it
expires 'too soon'