linux-kernel - Re: [ANNOUNCE] 3.8-rc6-nohz4

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Date:	Thu, 07 Feb 2013 12:00:47 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Alessio Igor Bogani <abogani@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Chris Metcalf <cmetcalf@...era.com>,
	Christoph Lameter <cl@...ux.com>,
	Geoff Levand <geoff@...radead.org>,
	Gilad Ben Yossef <gilad@...yossef.com>,
	Hakan Akkan <hakanakkan@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Li Zhong <zhong@...ux.vnet.ibm.com>,
	Namhyung Kim <namhyung.kim@....com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [ANNOUNCE] 3.8-rc6-nohz4

On Thu, 2013-02-07 at 17:41 +0100, Frederic Weisbecker wrote:

> I'm not convinced that "single task" must be a fundamental component
> of this. It's an implementation detail. We should be able to keep the
> tick off in the future when more than one task are on the runqueue and
> hrtick is on. May be this will never show up as a performance gain but
> we don't know yet.
> 
> Ok let's talk about that single task constraint in the Kconfig help so
> that the user knows the practical constraint as of today. But I
> suggest we keep that as an internal detail that we can deal with in
> the future.

Hmm, but isn't time slices still implemented by ticks? I would think
implementing multiple tasks would be another huge change.

Maybe have:

NO_HZ_IDLE
NO_HZ_SINGLE_TASK
NO_HZ_MULTI_TASK
NO_HZ_COMPLETE

And as Ingo has suggested, maybe in the future we can remove SINGLE and
MULTI and have just COMPLETE.

But anyway, the current method has a strict requirement of a single
task, and that is user visible. I would want to keep the config name
implying that requirement.

-- Steve


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