linux-kernel - Re: [PATCH 07/41] cpuset: Set up interface for nohz flag

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Date:	Tue, 08 May 2012 16:50:26 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Christoph Lameter <cl@...ux.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linaro-sched-sig@...ts.linaro.org,
	Alessio Igor Bogani <abogani@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Avi Kivity <avi@...hat.com>,
	Chris Metcalf <cmetcalf@...era.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Geoff Levand <geoff@...radead.org>,
	Gilad Ben Yossef <gilad@...yossef.com>,
	Hakan Akkan <hakanakkan@...il.com>,
	Ingo Molnar <mingo@...nel.org>, Kevin Hilman <khilman@...com>,
	Max Krasnyansky <maxk@...lcomm.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Stephen Hemminger <shemminger@...tta.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Sven-Thorsten Dietrich <thebigcorporation@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 07/41] cpuset: Set up interface for nohz flag

On Tue, 2012-05-08 at 16:20 +0200, Frederic Weisbecker wrote:
> 2012/5/7 Christoph Lameter <cl@...ux.com>:
> > On Tue, 1 May 2012, Frederic Weisbecker wrote:
> >
> >> Prepare the interface to implement the nohz cpuset flag.
> >> This flag, once set, will tell the system to try to
> >> shutdown the periodic timer tick when possible.
> >>
> >> We use here a per cpu refcounter. As long as a CPU
> >> is contained into at least one cpuset that has the
> >> nohz flag set, it is part of the set of CPUs that
> >> run into adaptive nohz mode.
> >
> > As I have said before: It would be much simpler if one could specify the
> > set of nohz cpus independently of cpusets. Having a flag f.e. as a file in
> >
> >        /sys/devices/system/cpu/cpuX/nohz
> 
> I don't know if it would be simpler. It's just a different interface
> to set a per-CPU property.
> Cpusets of sysfs, I don't mind either way.
> 
> What is the usual policy on where to put which kind of CPU property?

There's no such policy, but I don't get why Christoph objects to
cpusets, its the option I would prefer. You're going to use cpusets
anyway to partition your system, might as well also use it to mark a
whole partition/set as nohz.
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