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

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Date:	Tue, 14 Jun 2016 12:11:45 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	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


* 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.

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.

Thanks,

	Ingo