Re: power-efficient scheduling design

From: Arjan van de Ven
Date: Tue Jun 11 2013 - 21:49:08 EST

On 6/11/2013 5:27 PM, David Lang wrote:

Nobody is saying that this sort of thing should be in the fastpath of the scheduler.

But if the scheduler has a table that tells it the possible states, and the cost to get from the current state to each of these states (and to get back and/or wake up to
full power), then the scheduler can make the decision on what to do, invoke a routine to make the change (and in the meantime, not be fighting the change by trying to
schedule processes on a core that's about to be powered off), and then when the change happens, the scheduler will have a new version of the table of possible states and costs

This isn't in the fastpath, it's in the rebalancing logic.

the reality is much more complex unfortunately.
C and P states hang together tightly, and even C state on
one core impacts other cores' performance, just like P state selection
on one core impacts other cores.

(at least for x86, we should really stop talking as if the OS picks the "frequency",
that's just not the case anymore)

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