linux-kernel - Re: [PATCH 0/8] Suspend block api (version 7)

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Date:	Tue, 18 May 2010 16:06:36 -0700
From:	Arve Hjønnevåg <arve@...roid.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Brian Swetland <swetland@...gle.com>,
	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/8] Suspend block api (version 7)

2010/5/18 Rafael J. Wysocki <rjw@...k.pl>:
> On Wednesday 19 May 2010, Arve Hjønnevåg wrote:
>> 2010/5/18 Rafael J. Wysocki <rjw@...k.pl>:
>> > On Tuesday 18 May 2010, Arve Hjønnevåg wrote:
>> >> 2010/5/18 Rafael J. Wysocki <rjw@...k.pl>:
>> >> > On Tuesday 18 May 2010, Arve Hjønnevåg wrote:
>> >> >> On Mon, May 17, 2010 at 2:44 PM, Rafael J. Wysocki <rjw@...k.pl> wrote:
>> >> >> > On Monday 17 May 2010, Brian Swetland wrote:
>> >> >> >> On Mon, May 17, 2010 at 1:40 PM, Rafael J. Wysocki <rjw@...k.pl> wrote:
>> >> >> >> > On Monday 17 May 2010, Arve Hjønnevåg wrote:
>> >> >> >> >>
>> > ...
>> >>
>> >> > Now, to make it more "user-friendly", we can simply use
>> >> > queue_delayed_work() with a reasonable delay instead of queue_work() to queue
>> >> > the suspend work (the delay may be configurable via sysfs).
>> >> >
>> >>
>> >> I can add a delay (and the timeout support code does add a delay as an
>> >> optimization) to the unknown wakeup case, but this does not fix the
>> >> problem of a user turning on opportunistic suspend with a user space
>> >> framework that does not use suspend blockers. If the kernel uses
>> >> suspend blockers to make sure the wakeup event makes it to user space,
>> >> but user space does not block suspend, then the system will suspend
>> >> before the event is processed.
>> >
>> > But the user can still manually write to /sys/power/state. :-)
>> >
>>
>> Does adding or removing a delay change this? It seems in only changes
>> how quickly the user can finish that write.
>
> Yes, but that should allow the user to avoid rebooting the system if he does
> the "wrong thing".
>
>> I'm not convinced adding a configurable delay here is necessary.
>
> No, it's not, but it would be useful in some cases IMO.  Pretty much the same
> way your debug features are useful.
>
>> Once the driver that enabled the wakeup event has been updated to block
>> suspend until this event gets to user space, then this delay will
>> never be triggered. The kernel cannot tell the difference between a
>> user enabling opportunistic suspend but not wanting it and
>> opportunistic suspend aware user space code deciding that this wakeup
>> event should be ignored.
>
> The point is, if there's a delay, it may be too aggressive for some users and
> too conservative for some other users, so it makes sense to provide a means
> to adjust it to the user's needs.
>

My point is that the delay will not be used at all if the driver uses
a suspend blocker (like it should). Why add a configuration option for
opportunistic suspend that only works when the driver does not support
opportunistic suspend.

-- 
Arve Hjønnevåg
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