[tesla-dev] Dispatcher driven P-state management under simple policy

[Eric Saxe]

Hi Aubrey,

Li, Aubrey wrote:
> The policy seems not to be good.
> It prevents the core from going into idle. When the new kthread is idle
> thread,
> the policy will change the power state to low power state, this calls
> speedstep
> power interface on IA platform, which is implemented by xcall. the core
> may
> spend some time to grab highest mutex here.
>   
I'd like to see this done in a way that doesn't require the xcall. Is it 
possible to do the P-State transition such that one CPU (the current 
CPU), affects the whole P-state domain, eliminating the need for the xcall?

> P-state policy implemented in cmt thread switch here seems not to be a
> good
> idea. 
Are you saying this because a xcall would be needed?

> We can't upgrade or downgrade the speed level just by the old
> thread or
> the new thread is idle thread. 
That's the implementation of the current (rather naive) policy. It's 
really about utilization of the P-state domain, and currently that 
utilization is tracked by looking at transitions between idle and 
non-idle threads.

> We probably still need change it
> according to the
> system workload.
>   
Why not on a (P-state) domain by domain basis? We're trying to made some 
headway towards optimizing for larger systems that are only partially 
utilized....which is difficult to do considering the system wide workload...

Thanks,
-Eric

> Thanks,
> -Aubrey
>
>