From: "Rafael J. Wysocki" <rjw@rjwysocki.net>
To: Chirantan Ekbote <chirantan@chromium.org>
Cc: Alan Stern <stern@rowland.harvard.edu>,
        John Stultz <john.stultz@linaro.org>, Olof Johansson <olof@lixom.net>,
        Bastien Nocera <hadess@hadess.net>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        snanda@chromium.org, Tomeu Vizoso <tomeu.vizoso@collabora.com>,
        Linux PM list <linux-pm@vger.kernel.org>
Subject: Re: A desktop environment[1] kernel wishlist
Date: Wed, 06 May 2015 01:56:49 +0200
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On Tuesday, May 05, 2015 01:58:12 PM Chirantan Ekbote wrote:
> On Tue, May 5, 2015 at 12:35 PM, Alan Stern <stern@rowland.harvard.edu> wrote:
> > On Tue, 5 May 2015, Chirantan Ekbote wrote:
> >
> >> This is our plan for the next version (see my email earlier in this
> >> thread).  Keeping a hybrid power state with hacks in the drivers isn't
> >> really maintainable, scalable, or upstream-able and has caused us some
> >> headaches already.  Unfortunately we were working with the 3.14 kernel
> >> at the time, which didn't have the framework necessary to do anything
> >> else.  The new version of lucid sleep will have the power manager
> >> runtime suspend power-hungry devices before a suspend so that they
> >> remain powered off at resume time.  The power manager can then decide
> >> to resume those devices based on whether the wakeup event was
> >> user-triggered.
> >>
> >> Being able to determine the wakeup type from userspace is the only
> >> functionality we need from the kernel that doesn't already exist in
> >> mainline.
> >
> > Maybe you can simplify the problem.  You don't really need to know the
> > wakeup type, or to determine which device was responsible for the
> > wakeup.  All you really need to know is whether the wakeup was
> > user-triggered.  That may be much easier to discover.
> >
> 
> You are, of course, correct.  Ultimately the only requirement we have
> is that there exists a way for userspace to determine if the system
> woke up because of a user-triggered event.  The actual mechanism by
> which this determination is made isn't something I feel strongly
> about.  The reason I had been focusing on exposing the actual wakeup
> event to userspace is because classifying wakeup events as
> user-triggered or not feels to me like a policy decision that should
> be left to userspace.  If the kernel maintainers are ok with doing
> this work in the kernel instead and only exposing a binary yes/no bit
> to userspace for user-triggered wakeups, that's perfectly fine because
> it still meets our requirements.

Well, please see the message I've just sent.

All wakeup devices have a wakeup source object associated with them.  In
principle, we can expose a "priority" attribute from that for user space to
set as it wants to.  There may be two values of it, like "normal" and "high"
for example.

Then, what only remains is to introduce separate wakeup counts for the "high"
priority and "normal" priority wakeup sources and teach the power manager to
use them.

That leaves no policy in the kernel, but it actually has a chance to work.


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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