RE: [PATCH v1 2/2] intel_pstate: Change the setpoint for the cores

["Doug Smythies" <dsmythies@telus.net>]

On 2015.11.03 01:27 Philippe Longepe wrote:

> Change the setpoint to 60 accordingly to the new core busy scaled formula.
> The new formaula is based on the number of cycles per seconds
> (average frequency) divided by the requested frequency. So, we need to
> chose a setpoint more aggressive to improve performance.

Myself, and so as to improve response to some games and such that use
many threads and such but often a lower overall CPU load, I think the setpoint should be set a little lower.

There is a tradeoff in reducing the setpoint further as it increases the noise
and tendency to oscillate in the response curve. Ultimately, it may be desirable
to introduce a little slope in the load / CPU frequency response curve.

I have a bunch of graphs comparing response curves. [1]

>
> Measured with this parameter, we noticed an improvement in Browsermark
> for power and perf compared to the old formula:

I would like to try this test on my system. What is the exact test?
Do I understand correctly, that I need a browser to do the test?
(my test system is a server, and it doesn't have a browser.)

>
> Score without the patch: 3517
> Power without the patch: 6856 mW
>
> Score with the patch: 3719
> Power with the patch: 6265 mW

There are some other Phoronix tests that we (the original maintainer and
the a couple of others working with him used to use. See [1].

Please be aware that the last time I tried to bring back load based calculations,
Kristen tested the proposed solution on some intel "specpower test bed and
experienced a regression on haswell based server platforms vs.  Dirks
algorithm." I don't have any details.
Your response curve, and in particular your step function response time,
is different, so it might worth re-testing.
  
References:

[1] double u double u double u dot smythies dot com/~doug/linux/intel_pstate/philippe_longepe/index.html