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

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Date:	Thu, 7 Feb 2013 12:10:25 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	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>,
	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


* Steven Rostedt <rostedt@...dmis.org> wrote:

> I'll reply to this as I come up with comments.
> 
> First thing is, don't call it NO_HZ_FULL. A better name would 
> be NO_HZ_CPU. I would like to reserve NO_HZ_FULL when we 
> totally remove jiffies :-)

I don't think we want yet another config option named in a 
weird way.

What we want instead is to just split NO_HZ up into its 
conceptual parts:

   CONFIG_NO_HZ_IDLE
   CONFIG_NO_HZ_USER_SPACE
   CONFIG_NO_HZ_KERNEL_SPACE

Where the current status quo is NO_HZ_IDLE=y, and Frederic is 
about to introduce NO_HZ_USER_SPACE=y. When jiffies get removed 
we get NO_HZ_KERNEL_SPACE=y.

The 'CONFIG_NO_HZ' meta-option, which we should leave for easy 
configurability and for compatibility, should get us the 
currently recommended default, which for the time being might 
be:

   CONFIG_NO_HZ_IDLE=y
   # CONFIG_NO_HZ_USER_SPACE is disabled

Btw., you could add CONFIG_NO_HZ_KERNEL_SPACE right away, just 
keep it false all the time. That would document our future plans 
pretty well.

Once CONFIG_NO_HZ_USER_SPACE is proven problem-free, we might 
default to:

   CONFIG_NO_HZ_IDLE=y
   CONFIG_NO_HZ_USER_SPACE=y

The goal is to have this in the distant future:

   CONFIG_NO_HZ=y

   CONFIG_NO_HZ_IDLE=y
   CONFIG_NO_HZ_USER_SPACE=y
   CONFIG_NO_HZ_KERNEL_SPACE=y

And eventually we might even be able to get rid of all the 3 
variants, and only offer full-on/off.

Agreed?

Thanks,

	Ingo
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