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

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Message-ID: <AANLkTimHGpRAZklIwXu6wEbA3coKXJvCVLxj2twerkCw@mail.gmail.com>
Date:	Wed, 26 May 2010 03:17:23 -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.

2010/5/26 Peter Zijlstra <peterz@...radead.org>:
> On Wed, 2010-05-26 at 02:54 -0700, Arve Hjønnevåg wrote:
>>
>> 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.
>
> In particular I'm suggesting you ditch the /dev/suspend_block thing.
>
> With a single suspend manager process that manages the suspend state you
> can achieve the same goal.
>

Yes we don't need the /dev interface, but it is useful. Without it any
program that needs to block suspend has to make a blocking ipc call
into the suspend manager process. Android already does this for java
code, but system processes written in C block suspend directly with
the kernel since they cannot use the java APIs.

> When the suspend manager has a !0 busy-task count, it ensures the kernel
> won't auto-suspend, when it again reaches a 0 busy-task count, it
> re-instates the auto-suspend feature.
>
> That's pretty much what that device would do too.
>
> Ideally we would not do the auto-suspend thing at all and have
> runtime-PM improved. Not running apps when they expect to run is like
> the world turned upside down.
>
> 'Evil' apps could always report themselves as blocker anyway.
>

-- 
Arve Hjønnevåg
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