linux-kernel - Re: [PATCH 13/32] nohz: Adaptive tick stop and restart on nohz cpuset

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Message-ID: <1314718109.5812.13.camel@twins>
Date:	Tue, 30 Aug 2011 17:28:29 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Anton Blanchard <anton@....ibm.com>,
	Avi Kivity <avi@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
	Stephen Hemminger <shemminger@...tta.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tim Pepper <lnxninja@...ux.vnet.ibm.com>,
	Paul Menage <paul@...lmenage.org>
Subject: Re: [PATCH 13/32] nohz: Adaptive tick stop and restart on nohz
 cpuset

On Tue, 2011-08-30 at 16:38 +0200, Frederic Weisbecker wrote:
> On Tue, Aug 30, 2011 at 02:44:10PM +0200, Peter Zijlstra wrote:
> > On Mon, 2011-08-29 at 20:28 +0200, Frederic Weisbecker wrote:
> > > tick_nohz_stop_sched_tick() checks that
> > > with {rcu,printk,arch}_needs_cpu() and restores a periodic behaviour
> > > until nobody else needs the CPU. 
> > 
> > tick_nohz_stop_sched_tick() should not restore stuff, it should at worst
> > fail to stop but never enable that's just weird.
> 
> It's not really enablement, it's just nohz behaviour but the next tick is
> in HZ :o)
> 
> Like you said before it's an optimization. 

I'm still not feeling very confident about all that..

> I can do the things differently
> for idle and non-idle cases there but I'm not sure it's really a good thing.

its not, but I'm very sure I've lost you on why that should be the case.
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