linux-kernel - Re: [PATCH 1/8] PM: Add suspend block api.

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Message-ID: <20100527154152.GF1957@elf.ucw.cz>
Date:	Thu, 27 May 2010 17:41:52 +0200
From:	Pavel Machek <pavel@....cz>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Florian Mickler <florian@...kler.org>,
	Arve Hj??nnev??g <arve@...roid.com>,
	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	Len Brown <len.brown@...el.com>,
	Randy Dunlap <rdunlap@...otime.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <ak@...ux.intel.com>,
	Cornelia Huck <cornelia.huck@...ibm.com>,
	Tejun Heo <tj@...nel.org>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Magnus Damm <damm@...l.co.jp>,
	Nigel Cunningham <nigel@...onice.net>,
	Alan Stern <stern@...land.harvard.edu>,
	Ming Lei <tom.leiming@...il.com>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Maxim Levitsky <maximlevitsky@...il.com>,
	linux-doc@...r.kernel.org
Subject: Re: [PATCH 1/8] PM: Add suspend block api.

Hi!

> > > > Yeah, one file selects behavior of another file, and to read available
> > > > states for opportunistic, you have to write to file first.
> > > > 
> > > > I still don't like the interface.
> > > > 
> > > 
> > > Actually, what would be a better interface? 
> > > 
> > > I wonder why it is not like this:
> 
> Because I think the "forced" and "opportunistic" suspend "modes" are mutually
> exclusive in practice and the interface as proposed reflects that quite well.

Why should they be? Forced disk while opportunistic mem is active
makes a lot of sense. If code can't support it now, just return
-EINVAL, but please don't cripple the interface just because of that.

> > > /sys/power/state 
> > > 	no change, works with and without opportunistic suspend the
> > > 	same. Ignores suspend blockers. Really no change. (From user
> > > 	perspective)
> > > 
> > > /sys/power/opportunistic
> > > 	On / Off
> > > 	While Off the opportunistic suspend is off.
> > > 	While On, the opportunistic suspend is on and if there are no
> > > 	suspend blockers the system goes to suspend. 
> > > 
> > 
> > I forgot, of course there needs to be another knob to implement the
> > "on" behaviour  in the opportunistic mode
> > 
> >  /sys/power/block_opportunistic_suspend
> > 
> > There you have it. One file, one purpose. 
> 
> That's getting messy IMHO.
> 
> In addition to that you get a nice race when the user writes "mem"
> to /sys/power/state and opportunistic suspend happens at the same
> time.

It should not opportunistically suspend when it has work to do (like
entering forced suspend).
									Pavel

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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