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

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Date:	Thu, 21 Mar 2013 11:02:18 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Arjan van de Ven <arjan@...ux.intel.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	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 Thu, Mar 21, 2013 at 10:41:30AM -0700, Arjan van de Ven wrote:
> On 3/21/2013 10:18 AM, Paul E. McKenney wrote:
> >	o	Use the "idle=poll" boot parameter.  However, please note
> >		that use of this parameter can cause your CPU to overheat,
> >		which may cause thermal throttling to degrade your
> >		latencies --and that this degradation can be even worse
> >		than that of dyntick-idle.
> 
> it also disables (effectively) Turbo Mode on Intel cpus... which can cost you a serious percentage of performance

Thank you, added!  Please see below for the updated list.

							Thanx, Paul

------------------------------------------------------------------------

o	Dyntick-idle slows transitions to and from idle slightly.
	In practice, this has not been a problem except for the most
	aggressive real-time workloads, which have the option of disabling
	dyntick-idle mode, an option that most of them take.  However,
	some workloads will no doubt want to use adaptive ticks to
	eliminate scheduling-clock-tick latencies.  Here are some
	options for these workloads:

	a.	Use PMQOS from userspace to inform the kernel of your
		latency requirements (preferred).

	b.	Use the "idle=mwait" boot parameter.

	c.	Use the "intel_idle.max_cstate=" to limit the maximum
		depth C-state depth.

	d.	Use the "idle=poll" boot parameter.  However, please note
		that use of this parameter can cause your CPU to overheat,
		which may cause thermal throttling to degrade your
		latencies -- and that this degradation can be even worse
		than that of dyntick-idle.  Furthermore, this parameter
		effectively disables Turbo Mode on Intel CPUs, which
		can significantly reduce maximum performance.

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