linux-kernel - Re: [linux-pm] [PATCH 0/8] Suspend block api (version 6)

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Message-ID: <Pine.LNX.4.44L0.1005131756420.1731-100000@iolanthe.rowland.org>
Date:	Thu, 13 May 2010 18:01:33 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Tony Lindgren <tony@...mide.com>
cc:	Paul Walmsley <paul@...an.com>,
	Arve Hjønnevåg <arve@...roid.com>,
	Linux-pm mailing list <linux-pm@...ts.linux-foundation.org>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	Tejun Heo <tj@...nel.org>, Oleg Nesterov <oleg@...hat.com>,
	Kevin Hilman <khilman@...prootsystems.com>,
	<magnus.damm@...il.com>, Theodore Ts'o <tytso@....edu>,
	mark gross <mgross@...ux.intel.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Geoff Smith <geoffx.smith@...el.com>,
	Brian Swetland <swetland@...gle.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Matthew Garrett <mjg@...hat.com>,
	Benoît Cousson <b-cousson@...com>,
	<linux-omap@...r.kernel.org>, Vitaly Wool <vitalywool@...il.com>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Liam Girdwood <lrg@...mlogic.co.uk>
Subject: Re: [linux-pm] [PATCH 0/8] Suspend block api (version 6)

On Thu, 13 May 2010, Tony Lindgren wrote:

> > > And that's why 
> > > it should be handled by runtime power management instead.
> > 
> > Runtime PM is not capable of freezing userspace and shutting down CPUs.  
> > More or less by definition -- if it could then it wouldn't be "runtime" 
> > any more, since the processor wouldn't be running.
> 
> Not true. We are already powering off CPUs and rebooting them for
> at least omaps in every idle loop using cpuidle. The memory stays on.

Okay, that's a valid point.  But is that approach usable in general 
(i.e., on non-OMAP systems)?

How do you handle situations where the CPU is currently idle but an 
event (such as I/O completion) is expected to occur in the near future?  
You don't want to power-off and reboot then, do you?

Alan Stern

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