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

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Message-ID: <AANLkTikXy__71nBNW0EFbyL_qNf0nQ68pW9KymWlTk7L@mail.gmail.com>
Date:	Wed, 2 Jun 2010 11:05:18 -0700
From:	Brian Swetland <swetland@...gle.com>
To:	Neil Brown <neilb@...e.de>
Cc:	Arve Hjønnevåg <arve@...roid.com>,
	Thomas Gleixner <tglx@...utronix.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, Jun 2, 2010 at 1:06 AM, Neil Brown <neilb@...e.de> wrote:
> On Wed, 2 Jun 2010 00:05:14 -0700
> Arve Hjønnevåg <arve@...roid.com> wrote:
>> > The user-space suspend daemon avoids losing wake-events by using
>> > fcntl(F_OWNER) to ensure it gets a signal whenever any important wake-event
>> > is ready to be read by user-space.  This may involve:
>> >  - the one daemon processing all wake events
>>
>> Wake up events are not all processed by one daemon.
>
> Not with your current user-space code, no.  Are you saying that you are not
> open to any significant change in the Android user-space code?  That would
> make the situation a lot harder to resolve.

There are many wakeup events possible in a typical system --
keypresses or other input events, network traffic, telephony events,
media events (fill audio buffer, fill video decoder buffer, etc), and
I think requiring that all wakeup event processing bottleneck through
a single userspace process is non-optimal here.

The current suspend-blocker proposal already involves userspace
changes (it's different than our existing wakelock interface), and
we're certainly not opposed to any/all userspace changes on principle,
but on the other hand we're not interested in significant reworks of
userspace unless they actually improve the situation somehow.  I think
bottlenecking events through a central daemon would represent a step
backwards.

Brian
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