★ Session Summary ★ Scene setting (Morten) Workshop scheduled session wise update by attendees that ran/participated-in those sessions (Mike, Daniel, Nico, Morten, Dietmar). Key outcomes: - Understanding of what the maintainer opinion was on current work - Understanding on next steps for each track (EAS core, sched <-> PM interop, tools) Tools supporting EAS - Brief overview since there is already a detailed session earlier in the week: LCU14-206) - Idlestat, rtapp (Amit and Vincent) - Current status - Feature roadmap --------------------------------------------------- ★ Resources ★ Zerista: http://lcu14.zerista.com/event/member/137769 Google Event: https://plus.google.com/u/0/events/cssb4s1l4mrhjvga49jphg808o8 Presentation: http://www.slideshare.net/linaroorg/lcu14-402-kernel-summitupdatefinal-39262924 Video: https://www.youtube.com/watch?v=UhmfeCqQrxU&list=UUIVqQKxCyQLJS6xvSmfndLA Etherpad: http://pad.linaro.org/p/lcu14-402 --------------------------------------------------- ★ Event Details ★ Linaro Connect USA - #LCU14 September 15-19th, 2014 Hyatt Regency San Francisco Airport --------------------------------------------------- http://www.linaro.org http://connect.linaro.org

1. 1
Energy-aware Scheduling:
Kernel Summit workshop update
Linaro Connect CLU14, Burlingame,CA.
Morten Rasmussen

2. Workshop details
 Full-day workshop held at Kernel Summit 2014, August 19th
2014.
 Workshop goal:
 Coordinate plans for developing/improving energy-awareness in the
kernel scheduler and coordination with power management
frameworks.
 Attendees from the entire community including Intel, Google,
IBM, Linaro, QualComm, ARM.
 Summaries:
2
 http://lwn.net/Articles/609561/
 http://lwn.net/Articles/609969/ (detailed)

3. Workshop Agenda
Topics Owner
Benchmarking and testing energy improvements Daniel Lezcano (Linaro),
3
Mike Turquette (Linaro)
Task/cpu utilization tracking, compute capacity
representation and load/utilization tracking
improvements
Morten Rasmussen
(ARM)
Load tracking continued and scheduler/cpufreq
interaction
Mike Turquette (Linaro),
Preeti U Murthy (IBM)
Improving idle state selection Daniel Lezcano (Linaro),
Preeti U Murthy (IBM)
Platform performance/energy data/model in scheduler or
user-space
Morten Rasmussen
(ARM)
Power management in virtualized environments Preeti U Murthy (IBM)

4. Kernel Summit Summary slides
4

5. Energy-aware Scheduling Workshop
 Tools and benchmarks:
5
 Workload generation tool based on RT-app is under development by Linaro:
 Generates test patterns described used JSON
 Two workload descriptions available already: Android audio playback and
web broswing.
 Ftrace P- & C-state analysis tool (idlestat) by Linaro:
 Gathers power/energy related statistics
 Plans for integrating platform power model support to estimate energy
consumption.
 Outcome
 Community feedback on tools
 Extended and agree on suite of workload (JSON) descriptions so we can get
a common set of benchmarks.
 Limit scope to cpu energy consumption. There are no current proposals for
how to integrate memory, GPU, or other peripheral energy consumption.

6. Energy-aware Scheduling Workshop
 Load and utilization representation in the scheduler:
6
 Agreement on including a utilization metric in addition to the current
load tracking. The scheduler documentation needs to be updated with
terminology and concepts.
 Agreed that we need to make per-entity load tracking (and utilization)
scale invariant, i.e. factor in frequency scaling.
 Next step (and somewhat agreed) is to let the scheduler drive
frequency scaling (event driven) to get rid of existing sampling-based
governors (long term). The current cpufreq governors will continue to
exist while scheduler driven frequency scaling is being developed.
 Energy-awareness support must be optional (possible to compile
out/static_key) for platforms that don't care or have hardware magic
that can't cooperate with the OS.

7. Energy-aware Scheduling Workshop
 Energy model driven scheduling proposal:
7
 Techniques for energy-aware scheduling are not beneficial for all platforms.
 To avoid getting too many tunable heuristics that are nearly impossible for
non-scheduler developers to tune, it has been proposed to have a simple in-kernel
platform specific energy model.
 The model will be used to estimate the implications of scheduling decisions,
not provide accurate absolute energy estimates.
 The model is basically a set of P- and C-state tables, which should be
reasonable to ask platform vendors to provide. Alternatively, it should be
possible to extract on platforms where energy/power measurement is
possible.
 Concept RFC patch set for ARM TC2 is out. Needs to be tested on more
platforms.
 Model data to be provided by arch/* code. May come from DT, ACPI, or
driver.
 Agreement/no violent objections on continuing work on this idea.

8. Energy-aware Scheduling Workshop
 Idle-state awareness:
 Lack of scheduler idle-state awareness needs to be addressed.
Important for both PowerPC and ARM.
 Should be addressed as part of the energy model proposal.
 Work on better prediction of wakeup events discussed.
 Power policies under virtualization:
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 Communicating power management constraints from guest to host.
 Not desirable. Power management should be controlled only by the
host.