linux-kernel - Re: [linux-pm] Re: Hibernation considerations

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Message-ID: <877ioupxi8.fsf@jbms.ath.cx>
Date:	Fri, 20 Jul 2007 17:37:35 -0400
From:	Jeremy Maitin-Shepard <jbms@....edu>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	david@...g.hm, Milton Miller <miltonm@....com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Ying Huang <ying.huang@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-pm <linux-pm@...ts.linux-foundation.org>
Subject: Re: [linux-pm] Re: Hibernation considerations

Alan Stern <stern@...land.harvard.edu> writes:

> On Fri, 20 Jul 2007 david@...g.hm wrote:
>> > Userspace can submit I/O requests.  Someone will have to audit every
>> > driver to make sure that such I/O requests don't cause a quiesced
>> > device to become active.  If the device is active, it will make the
>> > memory snapshot inconsistent with the on-device data.
>> 
>> assuming this is the suspend-from-ram after a kexec back from the 
>> write-to-disk kernel I don't think you are correct.
>> 
>> when doing a suspend-to-ram you get to a point where you just don't use 
>> any userspace.

> What do you mean?  How can you prevent user tasks from running?  That's 
> basically what the freezer does, and the whole point of this approach 
> is to eliminate the freezer.  Right?

Presumably no tasks at all would be scheduled.

>> from that point on you are just walking the device tree 
>> putting things into low-power mode. This is the point where we are talking 
>> about jumping to.

> Yes.  And putting things into low-power mode requires the ability to 
> run the scheduler, which means that user tasks can be scheduled, which 
> means that they can run.

Does it really (fundamentally) require scheduling tasks, particularly in
the case that the devices have already been put in the "quiesced" state?

-- 
Jeremy Maitin-Shepard
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