linux-kernel - Re: [PATCH] nohz1: Documentation

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Date:	Thu, 21 Mar 2013 08:45:07 -0700
From:	Arjan van de Ven <arjan@...ux.intel.com>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	paulmck@...ux.vnet.ibm.com,
	Frederic Weisbecker <fweisbec@...il.com>,
	Rob Landley <rob@...dley.net>, linux-kernel@...r.kernel.org,
	josh@...htriplett.org, zhong@...ux.vnet.ibm.com,
	khilman@...aro.org, geoff@...radead.org, tglx@...utronix.de
Subject: Re: [PATCH] nohz1: Documentation

On 3/20/2013 5:27 PM, Steven Rostedt wrote:
> I'm not sure I would recommend idle=poll either. It would certainly
> work, but it goes to the other extreme. You think NO_HZ=n drains a
> battery? Try idle=poll.

do not ever use idle=poll on anything production.. really bad idea.

if you temporary cannot cope with the latency, you can use the PMQOS system
to limit (including going all the way to idle=poll).
but using idle=poll completely is very nasty for the hardware.

In addition we should document that idle=poll will cost you peak performance,
possibly quite a bit.

the same is true for the kernel paramter to some extend; it's there to work around
broken bioses/hardware/etc; if you have a latency/runtime requirement, it's much better
to use PMQOS for this from userspace.

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