linux-kernel - Re: A desktop environment[1] kernel wishlist

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Date:	Tue, 5 May 2015 16:38:35 -0700 (PDT)
From:	David Lang <david@...g.hm>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
cc:	Chirantan Ekbote <chirantan@...omium.org>,
	Alan Stern <stern@...land.harvard.edu>,
	John Stultz <john.stultz@...aro.org>,
	Olof Johansson <olof@...om.net>,
	Bastien Nocera <hadess@...ess.net>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	snanda@...omium.org, Tomeu Vizoso <tomeu.vizoso@...labora.com>,
	Linux PM list <linux-pm@...r.kernel.org>
Subject: Re: A desktop environment[1] kernel wishlist

On Wed, 6 May 2015, Rafael J. Wysocki wrote:

>> 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.

how about instead of setting two states and defining that one must be a subset 
of the other you instead have the existing feed of events and then allow 
software that cares to define additional feeds that take the current feed and 
filter it. We allow bpf filters in the kernel, so use those to filter what 
events the additional feed is going to receive.

remember that the interesting numbers in CS are 0, 1, and many, not 2 :-)

don't limit things to two feeds with one always being a subset of the other, 
create a mechanism to allow an arbitrary number of feeds that can be filtered in 
different ways

David Lang
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