linux-kernel - Re: [GIT PULL] nohz: Adaptively stop the tick, finally

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Message-ID: <20130424145017.GA6993@somewhere>
Date:	Wed, 24 Apr 2013 16:50:20 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	LKML <linux-kernel@...r.kernel.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>,
	Kevin Hilman <khilman@...aro.org>,
	Li Zhong <zhong@...ux.vnet.ibm.com>,
	Oleg Nesterov <oleg@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Stephane Eranian <eranian@...gle.com>,
	Jiri Olsa <jolsa@...hat.com>
Subject: Re: [GIT PULL] nohz: Adaptively stop the tick, finally

On Wed, Apr 24, 2013 at 09:38:52AM +0200, Ingo Molnar wrote:
> 
> * Ingo Molnar <mingo@...nel.org> wrote:
> 
> > One detail: 'make oldconfig' gave me:
> > 
> >  Timer tick handling
> >    1. Periodic timer ticks (constant rate, no dynticks) (HZ_PERIODIC) (NEW)
> >  > 2. Idle dynticks system (tickless idle) (NO_HZ_IDLE) (NEW)
> > 
> > I.e. CONFIG_NO_HZ_IDLE is picked by default. The default should really be 
> > CONFIG_HZ_PERIODIC - so that people can easily enable full dynticks but 
> > are not defaulted into it unknowingly.
> 
> Oh, I got confused by the artificial hiding of NO_HZ_FULL again. Why is it 
> still hidden? I have a fairly generic config, yet it was not offered. I 
> bet most people won't ever see it!
> 
> Sigh, it's due to the dependency mess that I pointed out twice already:
> 
>         depends on TREE_RCU || TREE_PREEMPT_RCU

Ok I just removed this one. This was the same as "depends on SMP" which we already
have.

>         depends on VIRT_CPU_ACCOUNTING_GEN
> 
> It should _really_ select both the RCU and the CPU time accounting model 
> automatically!

Yeah I know. I have yet to fix that in Kconfig (it's a Kconfig limitation).
It's high on my TODO list.

> 
> The selection of the dynticks mode certainly overrides RCU selection, and 
> it should for sure override some arcane, low level detail like the CPU 
> accounting model ...

Agreed, that was not intended to stay as is.

Thanks.
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