linux-kernel - Re: [RFC GIT PULL] nohz: Full dynticks rq clock handling

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Message-ID: <20130411151109.GC15699@somewhere>
Date:	Thu, 11 Apr 2013 17:11:13 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...nel.org>,
	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>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Paul Turner <pjt@...gle.com>, Mike Galbraith <efault@....de>
Subject: Re: [RFC GIT PULL] nohz: Full dynticks rq clock handling

On Wed, Apr 10, 2013 at 12:26:43PM +0200, Peter Zijlstra wrote:
> 
> Another thing I just noticed; our update_curr() assumes its called at
> least once every 4 odd seconds (2^32 ns like).
> 
> update_curr() is 'required' for things like task runtime stats and
> everything that hangs off of that like cputimers etc.
> 
> Now I'm not entirely sure how the nr_running==1 nohz case deals with
> this, but I can imagine it might take a while. In this case we might
> need to 'fix' update_curr() to not asume the time delta fits in 32
> bits.
> 

Good catch, this is not handled yet.
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