[Ksummit-discuss] Energy-aware Scheduling Workshop

[Morten Rasmussen <morten.rasmussen@arm.com>]

Hi,

Last year's Energy-Aware Scheduling workshop [1,2] was a good
opportunity for interested parties to discuss some of the open issues in
this area face to face. While work is still ongoing on many of the
topics that were discussed, it might be worth having workshop again this
year to follow up, revise the plans if necessary, and discuss topics
that were not covered last year.

Before submitting a workshop proposal to the Ksummit PC I would like to
probe the interest. IMO, it is important that we have scheduler
maintainers present.

Workshop topic proposals:

Test cases
Use-cases for high-end phones (which some of us care about) consist of
rather complex software stacks which are not suitable for quick patch
testing [3]. While we can't avoid testing using the full software stack
in the end, it would be useful to have configurable micro-benchmarks for
initial testing and to reproduce specific scheduling patterns from the
full use-case for debugging purposes.

Energy Evaluation
A hot topic last year. We need a way to evaluate energy-awareness
patches. Work has started on an idle state analysis tool [4], but we are
not there yet.

Platform Performance/Energy data
Currently the kernel has quite limited knowledge about energy costs of
the platform where it is running. Without this information it is rather
hard to make energy-efficient scheduling decisions. It seems that
various energy-saving techniques don't work equally well on all
platforms and might even depend on the use-case. Should we give the
kernel enough information to construct a simple energy-model to guide
decisions?

CPU utilization and cpu_power
The entity load tracking has given us a much better indication of
individual task loadi. However, priority scaling makes it less suitable
for low load scenarios [5] where we care more about actual cpu
utilization per task when trying to figure out an energy-efficient load
balance. Do we need entity utilization tracking as well? Related to this
topic is the representation of cpu compute capacity. The current
representation, cpu_power, can't deal with heterogeneous systems
correctly. Can we come up with a solution that can handle SMT, SMP, and
heterogeneous systems?


All comments and topic proposals are welcome.

Thanks,
Morten

[1] http://lwn.net/Articles/571414/
[2] http://etherpad.osuosl.org/energy-aware-scheduling-ks-2013
[3] https://lkml.org/lkml/2014/1/7/355
[4] https://lkml.org/lkml/2014/3/24/363
[5] https://lkml.org/lkml/2014/1/7/503