linux-kernel - Re: [PATCH 1/8] PM: Opportunistic suspend support.

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Message-ID: <AANLkTil9ZtMFxTfE6ITiFNOl4S1k3Lvdp5BPgGX7LJhw@mail.gmail.com>
Date:	Wed, 26 May 2010 02:54:37 -0700
From:	Arve Hjønnevåg <arve@...roid.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Florian Mickler <florian@...kler.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Alan Stern <stern@...land.harvard.edu>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Linux-pm mailing list <linux-pm@...ts.linux-foundation.org>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
	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>,
	Nigel Cunningham <nigel@...onice.net>,
	Ming Lei <tom.leiming@...il.com>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Maxim Levitsky <maximlevitsky@...il.com>,
	linux-doc@...r.kernel.org, Matthew Garrett <mjg59@...f.ucam.org>,
	Greg KH <gregkh@...e.de>, tytso@....edu,
	James Bottomley <James.Bottomley@...e.de>
Subject: Re: [PATCH 1/8] PM: Opportunistic suspend support.

On Wed, May 26, 2010 at 2:33 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Wed, 2010-05-26 at 11:23 +0200, Florian Mickler wrote:
>
>> There is polling, because the suspend manager in userspace doesn't have
>> the whole picture. i.e. it doesn't know if a suspend will be
>> successfull.
>> So for aggressive suspending as a powersave-feature you need to poll
>> (i.e. retry upon failure). because you don't want to stay unsuspended.
>
> Clearly if it fails, there something to be done, right? So whoever does
> the thing will communicate with the suspend manager that it's going to
> do and has finished doing its thing, at which point it will try again.
>

If you are talking about user-space code here, then that does not
work. Not all kernel events that need to block suspend make it to
user-space.

> That's event driven, not polled.
>
> Also, if you want you can keep the kernel-side auto-suspend side, and
> have the suspend manager clear on !0 and re-establish the auto-suspend
> state on 0.
>
> But you really don't need this device thingy.
>

I'm not sure what you are proposing that we use instead. Both
user-space and kernel code needs to block suspend. If we don't have
suspend blockers in the kernel then user-space needs to poll when a
driver blocks suspend by returning an error from its suspend hook.

-- 
Arve Hjønnevåg
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