Re: [RFC][PATCH v5 00/14] sched: packing tasks

[Peter Zijlstra]

On Mon, Nov 11, 2013 at 11:33:45AM +0000, Catalin Marinas wrote:
> My understanding from the recent discussions is that the scheduler
> should decide directly on the C-state (or rather the deepest C-state
> possible since we don't want to duplicate the backend logic for
> synchronising CPUs going up or down). This means that the scheduler
> needs to know about C-state target residency, wake-up latency (I think
> we can leave coupled C-states to the backend, there is some complex
> synchronisation which I wouldn't duplicate).
> 
> Alternatively (my preferred approach), we get the scheduler to predict
> and pass the expected residency and latency requirements down to a
> power driver and read back the actual C-states for making task
> placement decisions. Some of the menu governor prediction logic could
> be turned into a library and used by the scheduler. Basically what
> this tries to achieve is better scheduler awareness of the current
> C-states decided by a cpuidle/power driver based on the scheduler
> constraints.

Ah yes.. so I _think_ the scheduler wants to eventually know about idle
topology constraints. But we can get there in a gradual fashion I hope.

Like the package C states on x86 -- for those to be effective the
scheduler needs to pack tasks and keep entire packages idle for as long
as possible.


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