linux-kernel - Re: [PATCH v12 05/13] task_isolation: support CONFIG_TASK_ISOLATION

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Message-ID: <33dcf5bd-891d-653d-fcb4-7560075f7661@mellanox.com>
Date:	Wed, 18 May 2016 12:34:41 -0400
From:	Chris Metcalf <cmetcalf@...lanox.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Gilad Ben Yossef <giladb@...hip.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>, Tejun Heo <tj@...nel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Christoph Lameter <cl@...ux.com>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Andy Lutomirski <luto@...capital.net>,
	<linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v12 05/13] task_isolation: support
 CONFIG_TASK_ISOLATION_ALL

On 5/18/2016 9:35 AM, Peter Zijlstra wrote:
> On Tue, Apr 05, 2016 at 01:38:34PM -0400, Chris Metcalf wrote:
>> This option, similar to NO_HZ_FULL_ALL, simplifies configuring
>> a system to boot by default with all cores except the boot core
>> running in task isolation mode.
> Hurm, we still have that option? I thought we killed it, because random
> people set it and 'complain' their system misbehaves.

It's still in, as of 4.6 (and still in linux-next too).  I did receive
feedback saying the option was useful, when setting up a kernel to run
isolation apps on systems that may have a varying number of processsors,
since it means you don't need to tweak the boot arguments each time.

A different approach that I'd be happy to pursue would be to provide
a "clipping" version of cpulist_parse() that allows you to pass a boot
argument like "nohz_full=1-1000" and just clip off the impossible cpus.
We could then change "nohz_full=" and "task_isolation=" to use it.

-- 
Chris Metcalf, Mellanox Technologies
http://www.mellanox.com