lkml.org 
[lkml]   [2020]   [Aug]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH v2 2/5] cpufreq: intel_pstate: Always return last EPP value from sysfs
From
Date
On Mon, 2020-08-24 at 19:42 +0200, Rafael J. Wysocki wrote:
> From: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
>
> Make the energy_performance_preference policy attribute in sysfs
> always return the last EPP value written to it instead of the one
> currently in the HWP Request MSR to avoid possible confusion when
> the performance scaling algorithm is used in the active mode with
> HWP enabled (in which case the EPP is forced to 0 regardless of
> what value it has been set to via sysfs).

Why is this a good idea, I wonder. If there was a prior discussion,
please, point to it.

The general approach to changing settings via sysfs is often like this:

1. Write new value.
2. Read it back and verify that it is the same. Because there is no
better way to verify that the kernel "accepted" the value.

Let's say I write 'balanced' to energy_performance_preference. I read
it back, and it contains 'balanced', so I am happy, I trust the kernel
changed EPP to "balanced".

If the kernel, in fact, uses something else, I want to know about it
and have my script fail. Why caching the value and making my script
_think_ it succeeded is a good idea.

In other words, in my usage scenarios at list, I prefer kernel telling
the true EPP value, not some "cached, but not used" value.

Artem.

\
 
 \ /
  Last update: 2020-08-25 08:21    [W:0.149 / U:0.088 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site