Re: [patch v5 04/15] sched: add sched balance policies in kernel

From: Ingo Molnar
Date: Wed Feb 20 2013 - 10:41:13 EST

* Alex Shi <alex.shi@xxxxxxxxx> wrote:

> Now there is just 2 types policy: performance and
> powersaving(with 2 degrees, powersaving and balance).

I don't think we really want to have 'degrees' to the policies
at this point - we want each policy to be extremely good at what
it aims to do:

- 'performance' should finish jobs in in the least amount of
time possible. No ifs and whens.

- 'power saving' should finish jobs with the least amount of
watts consumed. No ifs and whens.

> powersaving policy will try to assign one task to each LCPU,
> whichever the LCPU is SMT thread or a core. The balance policy
> is also a kind of powersaving policy, just a bit less
> aggressive. It will try to assign tasks according group
> capacity, one task to one capacity.

The thing is, 'a bit less aggressive' is an awfully vague
concept to maintain on a long term basis - while the two
definitions above are reasonably deterministic which can be
measured and improved upon.

Those two policies and definitions are also much easier to
communicate to user-space and to users - it's much easier to
explain what each policy is supposed to do.

I'd be totally glad if we got so far that those two policies
work really well. Any further nuance visible at the ABI level is
I think many years down the road - if at all. Simple things
first - those are complex enough already.


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