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

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Date:	Mon, 13 Jun 2016 16:30:52 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Eric Dumazet <edumazet@...gle.com>
cc:	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.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
Subject: Re: [patch 13/20] timer: Switch to a non cascading wheel

On Mon, 13 Jun 2016, Eric Dumazet wrote:
> On Mon, Jun 13, 2016 at 5:30 AM, Thomas Gleixner <tglx@...utronix.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.
> >
> Anyway, for the more common HZ=1000 case, what would the 'limit' be ?

34 minutes with the currently chosen parameters.