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

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Message-ID: <20100531232617.GF31155@gvim.org>
Date:	Mon, 31 May 2010 16:26:17 -0700
From:	mark gross <640e9920@...il.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Arve Hjønnevåg <arve@...roid.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Florian Mickler <florian@...kler.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Linux PM <linux-pm@...ts.linux-foundation.org>,
	Brian Swetland <swetland@...gle.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	markgross@...gnar.org
Subject: Re: [linux-pm] [PATCH 0/8] Suspend block api (version 8)

On Mon, May 31, 2010 at 11:38:55PM +0200, Rafael J. Wysocki wrote:
> On Monday 31 May 2010, Arve Hjønnevåg wrote:
> > 2010/5/29 Alan Stern <stern@...land.harvard.edu>:
> > > On Sat, 29 May 2010, Arve Hjønnevåg wrote:
> > >
> > >> > In place of in-kernel suspend blockers, there will be a new type of QoS
> > >> > constraint -- call it QOS_EVENTUALLY.  It's a very weak constraint,
> > >> > compatible with all cpuidle modes in which runnable threads are allowed
> > >> > to run (which is all of them), but not compatible with suspend.
> > >> >
> > >> This sound just like another API rename. It will work, but given that
> > >> suspend blockers was the name least objectionable last time around,
> > >> I'm not sure what this would solve.
> > >
> > > It's not just a rename.  By changing this into a QoS constraint, we
> > > make it more generally useful.  Instead of standing on its own, it
> > > becomes part of the PM-QOS framework.
> > >
> > 
> > We cannot use the existing pm-qos framework. It is not safe to call
> > from atomic context.
> 
> We've just merged a patch that fixed that if I'm not mistaken.  Mark, did your
> PM QoS update fix that?
>

I'm pretty sure it can be called in atomic context, and if its not I'm
sure we can fix that.  It can be called in atomic context.  I don't
think it was ever a problem to call it in atomic context.  The problem it
had was that crappy list of string compares.  Thats been fixed.

--mgross
 
> > Also, it does not have any state constraints, so it iterates over every
> > registered constraint each time one of them changes.
> 
> That's fixable IMO.
> 
> > Nor does is currently provide any stats for debugging.
> 
> That's why Alan is proposing to add that.
> 
> > The original wakelock patchset supported a wakelock type so it could
> > be used to block more then suspend, but I had to remove this because
> > it "overlapped" with pm-qos. So, yes I do consider this just another
> > rename.
> 
> It's an extension of an existing framework rather than an addition of a new
> one, with entirely new API and so on.  Extending existing APIs is much
> preferred to adding new ones, in general.
> 
> Rafael
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