linux-kernel - Re: [PATCH] - race-free suspend. Was: Re: [linux-pm] [PATCH 0/8] Suspend block api (version 8)

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Date:	Wed, 2 Jun 2010 11:33:05 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Arve Hjønnevåg <arve@...roid.com>
cc:	Neil Brown <neilb@...e.de>, "Rafael J. Wysocki" <rjw@...k.pl>,
	Alan Stern <stern@...land.harvard.edu>,
	Felipe Balbi <felipe.balbi@...ia.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"Paul@...p1.linux-foundation.org" <Paul@...p1.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Florian Mickler <florian@...kler.org>,
	Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
	Linux PM <linux-pm@...ts.linux-foundation.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	James Bottomley <James.Bottomley@...e.de>
Subject: Re: [PATCH] - race-free suspend. Was: Re: [linux-pm] [PATCH 0/8]
 Suspend block api (version 8)

On Wed, 2 Jun 2010, Arve Hjønnevåg wrote:
> 2010/6/2 Neil Brown <neilb@...e.de>:
> > There would still need to be some sort of communication between the the
> > suspend daemon on any event daemon to ensure that the events had been
> > processed.  This could be very light weight interaction.  The point though is
> > that with this patch it becomes possible to avoid races.  Possible is better
> > than impossible.
> >
> 
> We already have a solution. I don't think rejecting our solution but
> merging a worse solution should be the goal.

That's not the goal at all. We want a solution which is acceptable for
android and OTOH does not get into the way of other approaches.

The main problem I have is that suspend blockers are only addressing
one particular problem space of power management.

We have more requirements than that, e.g. an active device transfer
requires to prevent the idle code to select a deep power state due to
latency requirements. 

So we then have to implement two mechanisms in the relevant drivers:

   1) telling the idle code to limit latency
   2) telling the suspend code not to suspend

My main interest is to limit it to one mechanism, which is QoS based
and let idle and suspend make the appropriate decisions based on that
information.

Thanks,

	tglx