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

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Date:	Thu, 27 May 2010 19:42:41 +0200
From:	Florian Mickler <florian@...kler.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Arve Hjønnevåg <arve@...roid.com>,
	Vitaly Wool <vitalywool@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Paul@...p1.linux-foundation.org, felipe.balbi@...ia.com,
	Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
	Linux PM <linux-pm@...ts.linux-foundation.org>
Subject: Re: [linux-pm] [PATCH 0/8] Suspend block api (version 8)

On Thu, 27 May 2010 19:25:27 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> On Thu, 2010-05-27 at 19:21 +0200, Florian Mickler wrote:
> > On Thu, 27 May 2010 18:45:25 +0200 (CEST)
> > Thomas Gleixner <tglx@...utronix.de> wrote:
> > 
> > > The whole notion of treating suspend to RAM any different than a plain
> > > idle C-State is wrong. It's not different at all. You just use a
> > > different mechanism which has longer takedown and wakeup latencies and
> > > requires to shut down stuff and setup extra wakeup sources.
> > > 
> > > And there is the whole problem. Switching from normal event delivery
> > > to those special wakeup sources. That needs to be engineered in any
> > > case carefuly and it does not matter whether you add suspend blockers
> > > or not.
> > 
> > Ok, I just don't know the answer: How is it just another idle state if
> > the userspace gets frozen? Doesn't that bork the whole transition and
> > you need a userspace<->kernel synchronisation point to not loose events?
> 
> There is no userspace to freeze when the runqueues are empty.

If in the imaginery situation where userspace can aquire certain
wakeup-constraints and loose certain wakeup-constraints, then it could
be that the system enters suspend without empty runqueues. 

> And as explained, you won't loose events if all the devices do a proper
> state transition. To quote:

I believe the problem beeing userspace frozen at an unopportune time.
So the wakeup event is processed (kernel-side) but userspace didn't
have time to reacquire the correct wakeup-constraint to process the
event.

I.e. the wakeup will be effectivly ignored.


Cheers,
Flo
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