linux-kernel - Re: [PATCH 4/4] nohz: New option to force all CPUs in full dynticks range

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Message-ID: <5164160D.7080201@windriver.com>
Date:	Tue, 9 Apr 2013 09:22:21 -0400
From:	Paul Gortmaker <paul.gortmaker@...driver.com>
To:	Christoph Lameter <cl@...ux.com>
CC:	Ingo Molnar <mingo@...nel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Chris Metcalf <cmetcalf@...era.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>,
	Namhyung Kim <namhyung.kim@....com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 4/4] nohz: New option to force all CPUs in full dynticks
 range

On 13-04-08 10:57 AM, Christoph Lameter wrote:
> I think we could simplify things quite a bit if we either
> 
> 1. Add any cpus specified with nohz_full/extended=xxx to
> rcu_nocb. No check is then necessary anymore.
> 
> or
> 
> 2. Avoid the setting of cpus entirely? If full nohz mode is desired
> then pick one cpu (f.e. the first one or the one that is used for xtime
> updates) and then make all other cpus nohz. Set the affinity mask for the
> rcuoXXX threads to that cpu.

I can imagine people with multi socket systems wanting to have
a system partitioned with one "normal" core per physical socket,
for timekeeping, RCU threads, etc, but #2 would prevent that.

Paul.
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