linux-kernel - RE: [RFC] Splitting scheduler into two halves

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Date:	Mon, 3 Mar 2014 09:56:55 +0000
From:	"Du, Yuyang" <yuyang.du@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>,
	Morten Rasmussen <morten.rasmussen@....com>
CC:	Ingo Molnar <mingo@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"Van De Ven, Arjan" <arjan.van.de.ven@...el.com>,
	"Brown, Len" <len.brown@...el.com>,
	"Wysocki, Rafael J" <rafael.j.wysocki@...el.com>
Subject: RE: [RFC] Splitting scheduler into two halves

Well, my two cents in response (sorry, I will use a Linux style mail client next time):

1) Top half and bottom half do have interaction with each other. They share information, top half provides some measurement/average to load balance. Good news is they don't interleave operation. Splitting them does not mean they must be self-inclusive to each other.

2) What I have done is a starting point. What really matters is some good design from that starting point. I myself have been working on workload consolidation (or task packing, you name it) for a while. I did have an intent to do a complete bottom half. So, encapsulating the load balance in a class allows it to be replaced easier. But this had already been the last thing I want even if I can do that (before the very first email), because it won't make "a better world".

Lets explore the design space a little bit. For load balance, its function is like:

Tasks -> be balanced -> on CPUs

Be more specific:

[ which_1 ] tasks -> be balanced -> on [ which_2 ] CPUs

Which_1 can be: fair or rt by priority. ARM people may want "small/light" or "big/heavy" by load tracking (fortunately, we don't need that). Maybe others.

Which_2 can be: all, or some.

Which_1 * which_2 have many combinations, each of which has this in common: XX tasks -> be balanced -> on YY CPUs (XX defined by bottom half but got from top half, the other done by bottom half).

So it looks like we need a class, and we need a few implementations (each for a combination) in a *hierarchy* and work together.

I don't have the final answer yet, this is why I said I am continuing to redesign and refactor it. But it really looks that modularity should/can be applied here to help realize so complex a system.

Thanks,
Yuyang
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