Re: [RFC PATCH 3/3] idle: store the idle state index in the structrq

[Arjan van de Ven]

On 2/3/2014 4:54 AM, Morten Rasmussen wrote:

> I'm therefore not convinced that idle state index is the right thing to
> give the scheduler. Using a cost metric would be better in my
> opinion.


I totally agree with this, and we may need two separate cost metrics

1) A latency driven one
2) A performance impact on

first one is pretty much the exit latency related time, sort of a "expected time to first instruction"
(currently menuidle has the 99.999% worst case number, which is not useful for this, but is a first
approximation). This is obviously the dominating number for expected-short running tasks

second on is more of a "is there any cache/TLB left or is it flushed" kind of metric. It's more tricky
to compute, since what is the cost of an empty cache (or even a cache migration) after all....
.... but I suspect it's in part what the scheduler will care about more for expected-long  running tasks.




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