linux-kernel - Re: [linux-pm] Re: [PATCH] Remove process freezer from suspend to RAM pathway

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Message-Id: <200707031651.10225.rjw@sisk.pl>
Date:	Tue, 3 Jul 2007 16:51:09 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Johannes Berg <johannes@...solutions.net>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	linux-kernel@...r.kernel.org, Pavel Machek <pavel@....cz>,
	linux-pm@...ts.linux-foundation.org
Subject: Re: [linux-pm] Re: [PATCH] Remove process freezer from suspend to RAM pathway

On Tuesday, 3 July 2007 16:21, Johannes Berg wrote:
> On Tue, 2007-07-03 at 14:56 +0200, Rafael J. Wysocki wrote:
> 
> > Still, can you please read this post from Alan Stern:
> > 
> > https://lists.linux-foundation.org/pipermail/linux-pm/2007-June/012847.html
> > 
> > ?  I don't think I'm able to repeat the arguments given in there in a
> > convincing way.
> 
> As I read it, Alan basically has two objections:
>  (1) drivers shouldn't need to worry about this
>  (2) suspend should be transparent to userspace
> 
> His proposed solution (freezing tasks when they cross the kernel
> boundary) helps for the s-t-r case, but in fact doesn't solve (1)
> because devices can be suspended at runtime

This is a different thing and a different infrastructure is needed for it (not
present at the moment).

> and then you certainly do not want to freeze tasks that try to access the
> device. 
> 
> (2) is related but not identical, what if you have a device suspended at
> runtime and some tasks tries to access it; should the task block until
> you wake up that device?

I think the device should be woken up in that case.

> I think the core of the discussion isn't appreciated by everybody here
> yet---we need to solve both run-time and suspend-to-ram-time device
> suspend, not just one of them.

For now, we're discussing the suspend-to-ram-time suspend only, for which
we have (some) infrastrcuture (and which should be supported by all drivers,
IMO).

Greetings,
Rafael


-- 
"Premature optimization is the root of all evil." - Donald Knuth
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