linux-kernel - Re: [PATCH 0/8] Suspend block api (version 6)

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Date:	Wed, 5 May 2010 16:42:29 -0700
From:	Brian Swetland <swetland@...gle.com>
To:	Kevin Hilman <khilman@...prootsystems.com>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	Matthew Garrett <mjg@...hat.com>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Arve Hjønnevåg <arve@...roid.com>,
	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	Tejun Heo <tj@...nel.org>, Oleg Nesterov <oleg@...hat.com>,
	Paul Walmsley <paul@...an.com>, magnus.damm@...il.com,
	mark gross <mgross@...ux.intel.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Geoff Smith <geoffx.smith@...el.com>
Subject: Re: [PATCH 0/8] Suspend block api (version 6)

On Wed, May 5, 2010 at 4:03 PM, Kevin Hilman
<khilman@...prootsystems.com> wrote:
>
> I guess what we're talking about here is a set of per-device
> constraints that could be used by both [opportunistic|system] suspend
> and runtime PM.  For lack of a better term, per-device PM QoS (as
> compared to the current system-wide PM QoS.)
>
> For example, if userspace (or some other device) has communicated that
> it has a constraint on the audio HW, then both the suspend path and the
> runtime PM path could check those constraints before making a decision
> on how to act.  Hopefully the phone app would set a constraint and the
> cow-noise app would not.  :)
>
> On OMAP, we keep track of per-device constraints (currently latency
> and throughput) in order to make proper run-time PM decicions in the
> kernel, but we are realizing that we need a way for userspace to
> communicate these constraints as well, so that userspace can make
> power vs. performance policy decisions instead of the kernel.
>
> Probably generalizing these into the LDM is the direction to go so
> userspace can set constraints on a per-device (or per-class?) basis:
>
> /sys/devices/.../power/constraint/throughput
> /sys/devices/.../power/constraint/wakeup_latency
> /sys/devices/.../power/constraint/... ?

The constraint stuff is definitely something I'd love to talk about in
detail.  It's a problem that I think is common to every SoC I've
worked with.  Having a general solution for this problem (of
specifying and observing various constraints for clock, power, qos,
etc) kernel-wide would seem like a big win.

Might be worth kicking some design ideas around and getting a bunch of
the interested parties together at some of the upcoming linux
conference things this fall on the east coast?

Brian
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