Re: [RFC PATCH 06/16] arm: topology: Define TC2 sched energy and provide it to scheduler

[Yuyang Du]

On Tue, Jun 10, 2014 at 12:16:22PM +0200, Peter Zijlstra wrote:
> What other target would you optimize for? The purpose here is to build
> an energy aware scheduler, one that schedules tasks so that the total
> amount of energy, for the given amount of work, is minimal.
> 
> So we can't measure in Watt, since if we forced the CPU into the lowest
> P-state (or even C-state for that matter) work would simply not
> complete. So we need a complete energy term.
> 
> Now. IPC is instructions/cycle, Watt is Joule/second, so IPC/Watt is
> 
> instructions   second
> ------------ * ------ ~ instructions / joule
>   cycle        joule
> 
> Seeing how both cycles and seconds are time units.
> 
> So for any given amount of instructions, the work needs to be done, we
> want the minimal amount of energy consumed, and IPC/Watt is the natural
> metric to measure this over an entire workload.

Ok, I understand. Whether we take IPC/watt as an input metric in scheduler or
as a goal for scheduler, we definitely need to try both.

Thanks, Peter.

Yuyang
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