linux-kernel - Re: [PATCH 3/7] idle, thermal, acpi: Remove home grown idle implementations

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Message-ID: <20131122171727.GT4138@linux.vnet.ibm.com>
Date:	Fri, 22 Nov 2013 09:17:27 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Jacob Pan <jacob.jun.pan@...ux.intel.com>,
	Arjan van de Ven <arjan@...ux.intel.com>, lenb@...nel.org,
	rjw@...ysocki.net, Eliezer Tamir <eliezer.tamir@...ux.intel.com>,
	Chris Leech <christopher.leech@...el.com>,
	David Miller <davem@...emloft.net>, rui.zhang@...el.com,
	Mike Galbraith <bitbucket@...ine.de>,
	Ingo Molnar <mingo@...nel.org>, hpa@...or.com,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: [PATCH 3/7] idle, thermal, acpi: Remove home grown idle
 implementations

On Fri, Nov 22, 2013 at 12:33:00PM +0100, Peter Zijlstra wrote:
> On Thu, Nov 21, 2013 at 08:20:36PM -0800, Paul E. McKenney wrote:
> > The 6ms to 25ms range should be just fine as far as normal RCU grace
> > periods are concerned.  However, it does mean that expedited grace
> > periods could be delayed: They normally take a few tens of microseconds,
> > but if they were unlucky enough to show up during an idle injection,
> > they would be magnified by two to three orders of magnitude, which is
> > not pretty.
> > 
> > Hence my suggestion of hooking into RCU on idle-injection start and end
> > so that RCU considers that time period to be idle.  Just like it does
> > for user-mode execution on NO_HZ_FULL kernels, so I still don't see this
> > approach to be a problem.  I must confess that I still don't understand
> > what Arjan doesn't like about it.
> 
> Using these patches it would indeed use the RCU idle machinery as per
> the normal idle path.

OK, sorry for my confusion!

> If you can I can add more WARN_ON()s in play_idle() to ensure we're not
> called while holding any RCU locks.

An rcu_sleep_check() or something similar, please!

							Thanx, Paul

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