Re: [Ksummit-discuss] [TECH(CORE?) TOPIC] Energy conservation bias interfaces

From: Paul Gortmaker <paul.gortmaker@windriver.com>
To: "Rafael J. Wysocki" <rjw@rjwysocki.net>,
	<ksummit-discuss@lists.linuxfoundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Len Brown <len.brown@intel.com>,
	Daniel Lezcano <daniel.lezcano@linaro.org>,
	Ingo Molnar <mingo@kernel.org>
Subject: Re: [Ksummit-discuss] [TECH(CORE?) TOPIC] Energy conservation bias interfaces
Date: Wed, 7 May 2014 17:03:37 -0400	[thread overview]
Message-ID: <536A9FA9.3030705@windriver.com> (raw)
In-Reply-To: <1998761.B2k0A5OtQR@vostro.rjw.lan>

On 14-05-06 08:54 AM, Rafael J. Wysocki wrote:
> Hi All,
> 
> During a recent discussion on linux-pm/LKML regarding the integration of the
> scheduler with cpuidle (http://marc.info/?t=139834240600003&r=1&w=4) it became
> apparent that the kernel might benefit from adding interfaces to let it know
> how far it should go with saving energy, possibly at the expense of performance.

These links from last year might be of general interest:

http://lwn.net/Articles/571414/

http://etherpad.osuosl.org/energy-aware-scheduling-ks-2013

Paul.
--

> 
> First of all, it would be good to have a place where subsystems and device
> drivers can go and check what the current "energy conservation bias" is in
> case they need to make a decision between delivering more performance and
> using less energy.  Second, it would be good to provide user space with
> a means to tell the kernel whether it should care more about performance or
> energy.  Finally, it would be good to be able to adjust the overall "energy
> conservation bias" automatically in response to certain "power" events such
> as "battery is low/critical" etc.
> 
> It doesn't seem to be clear currently what level and scope of such interfaces
> is appropriate and where to place them.  Would a global knob be useful?  Or
> should they be per-subsystem, per-driver, per-task, per-cgroup etc?
> 
> It also is not particularly clear what representation of "energy conservation
> bias" would be most useful.  Should that be a number or a set of well-defined
> discrete levels that can be given names (like "max performance", "high
> prerformance", "balanced" etc.)?  If a number, then what units to use and
> how many different values to take into account?
> 
> The people involved in the scheduler/cpuidle discussion mentioned above were:
>  * Amit Kucheria
>  * Ingo Molnar
>  * Daniel Lezcano
>  * Morten Rasmussen
>  * Peter Zijlstra
> and me, but I think that this topic may be interesting to others too (especially
> to Len who proposed a global "enefgy conservation bias" interface a few years ago).
> 
> Please let me know what you think.
> 
> Kind regards,
> Rafael
> 
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