linux-kernel - Re: [RFD] Automatic suspend

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Message-ID: <d6200be20902201759x7bcf3762k596d543db51ef104@mail.gmail.com>
Date:	Fri, 20 Feb 2009 17:59:32 -0800
From:	Arve Hjønnevåg <arve@...roid.com>
To:	Oliver Neukum <oliver@...kum.org>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Alan Stern <stern@...land.harvard.edu>,
	"Woodruff, Richard" <r-woodruff2@...com>,
	Arjan van de Ven <arjan@...radead.org>,
	Kyle Moffett <kyle@...fetthome.net>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>, Pavel Machek <pavel@....cz>,
	Nigel Cunningham <nigel@...el.suspend2.net>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	mark gross <mgross@...ux.intel.com>,
	Uli Luckas <u.luckas@...d.de>,
	Igor Stoppa <igor.stoppa@...ia.com>,
	Brian Swetland <swetland@...gle.com>,
	Len Brown <lenb@...nel.org>
Subject: Re: [RFD] Automatic suspend

On Fri, Feb 20, 2009 at 3:20 PM, Oliver Neukum <oliver@...kum.org> wrote:
> Am Samstag 21 Februar 2009 00:11:28 schrieb Arve Hjønnevåg:
>> On Fri, Feb 20, 2009 at 2:05 PM, Oliver Neukum <oliver@...kum.org> wrote:
>> > Am Freitag 20 Februar 2009 11:46:55 schrieb Rafael J. Wysocki:
>> >> On Thursday 19 February 2009, Oliver Neukum wrote:
>
>> > With the set of runnable processes.There's always a window between
>> > evaluating the current set of runnable tasks and telling the kernel to
>> > sleep. IMO the most elegant solution would be a task attribute that would
>> > signal the kernel that a task should not count as keeping the system busy
>> > even if it is runnable and trigger the sleep in kernel space.
>>
>> It is not always safe to enter suspend when no tasks are runnable. For
>> instance, a key event could be on a user space queue, but the code
>> that reads from that queue has been paged out.
>
> In that case you'd have a task waiting for IO. The driver should refuse
> to suspend or wake up the system as IO is completed. It may be
> inefficient to suspend for such a presumably short time, but it is not
> a correctness issue.

In that case, yes. My point was that no-runnable-tasks is not a
sufficient indicator of whether suspend should fail or not. We have no
control of what a user space thread is waiting for though. It could be
waiting on a mutex that is locked by a thread that is marked not to
prevent suspend.


-- 
Arve Hjønnevåg
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