lkml.org 
[lkml]   [2016]   [Feb]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [PATCH v10 1/3] cpufreq: Add mechanism for registering utilization update callbacks
Date
On Friday, February 19, 2016 09:28:23 AM Steve Muckle wrote:
> On 02/19/2016 08:42 AM, Srinivas Pandruvada wrote:
> > We did experiments using util/max in intel_pstate. For some benchmarks
> > there were regression of 4 to 5%, for some benchmarks it performed at
> > par with getting utilization from the processor. Further optimization
> > in the algorithm is possible and still in progress. Idea is that we can
> > change P-State fast enough and be more reactive. Once I have good data,
> > I will send to this list. The algorithm can be part of the cpufreq
> > governor too.
>
> There has been a lot of work in the area of scheduler-driven CPU
> frequency selection by Linaro and ARM as well. It was posted most
> recently a couple months ago:
>
> http://thread.gmane.org/gmane.linux.power-management.general/69176
>
> It was also posted as part of the energy-aware scheduling series last
> July. There's a new RFC series forthcoming which I had hoped (and
> failed) to post prior to my business travel this week; it should be out
> next week. It will address the feedback received thus far along with
> locking and other things.
>
> The scheduler hooks for utilization-based cpufreq operation deserve a
> lot more debate I think. They could quite possibly have different
> requirements than hooks which are chosen just to guarantee periodic
> callbacks into sampling-based governors.

Yes, they could.

The point here, though, is that even the sampling-based governors may
benefit from using the numbers provided by the scheduler instead of trying
to come up with analogous numbers themselves.

> For my part I think it would be best if the util/max parameters are
> omitted

OK, so please see the patch I've just sent to Juri:

https://patchwork.kernel.org/patch/8364621/

> until it's clear whether these same hooks can be effectively
> used for architecture agnostic scheduler-guided (capacity driven) CPU
> frequency support.

Well, if they can't, then we'll need to move the hooks, but I'm not sure
how this is related to the arguments they take.

> My upcoming RFC will provide another opportunity to debate the hooks as
> well as how scheduler-guided CPU frequency should be structured.

OK, looking forward to seeing the RFC then. :-)

Thanks,
Rafael

\
 
 \ /
  Last update: 2016-02-19 23:41    [W:0.283 / U:0.364 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site