Re: [Ksummit-discuss] [TECH(CORE?) TOPIC] Energy conservation bias interfaces

["Iyer, Sundar" <sundar.iyer@intel.com>]

> -----Original Message-----
> From: Preeti U Murthy [mailto:preeti@linux.vnet.ibm.com]
> Sent: Monday, May 12, 2014 10:43 PM
> To: Morten Rasmussen
> 
> You are right. We shouldn't be exposing so many knobs to user-space and
> expect the kernel to make good decisions based on these knobs being
> tweaked by user space. How about a high level classification of profiles like
> balanced, performance, powersave? These alone can be chosen by the user
> and the lower end tunings left to the discretion of the kernel.

Also, may I suggest to try to limit the discussion preliminary to CPU only? Should
we try to see if we can get a detailed policy, conditions specifically w.r.t CPU scheduling?

I am trying to sum up thoughts in my mind; please correct/add/edit as needed.

Scheduler options:
a. Spread wide: Utilize as much as CPUs as possible for tasks
b. Limit Local: Utilize as less as CPUs as possible.

Resources impacting these options:
a. if CPUs share common resources like power;
b. if CPUs share common cache; OIOW, cost of moving data around CPUs
c. CPU Energy efficiency profiles (BIG or little or xyz)

Factors affecting these options:

Ideally, we would like to spread wide if:
a. tasks/processes are heavily multi-threaded and parallelized;
b. asynchronous tasks that are single threaded and shifting them to multiple CPUs will
avoid boosting CPU load and hence P-states;
c. there is explicit hint from the application/user space about lack of data dependency;

does the list seem good to start?

Cheers!