linux-kernel - Re: [PATCH v1 07/16] thermal: gov_power_allocator: Eliminate a redundant variable

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Date: Tue, 23 Apr 2024 20:05:37 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Daniel Lezcano <daniel.lezcano@...aro.org>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, "Rafael J. Wysocki" <rjw@...ysocki.net>, 
	Linux PM <linux-pm@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, 
	Lukasz Luba <lukasz.luba@....com>, 
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Subject: Re: [PATCH v1 07/16] thermal: gov_power_allocator: Eliminate a
 redundant variable

On Tue, Apr 23, 2024 at 8:00 PM Daniel Lezcano
<daniel.lezcano@...aro.org> wrote:
>
> On 23/04/2024 19:54, Rafael J. Wysocki wrote:
> > On Tue, Apr 23, 2024 at 7:35 PM Daniel Lezcano
> > <daniel.lezcano@...aro.org> wrote:
> >>
> >> On 10/04/2024 18:12, Rafael J. Wysocki wrote:
> >>> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> >>>
> >>> Notice that the passive field in struct thermal_zone_device is not
> >>> used by the Power Allocator governor itself and so the ordering of
> >>> its updates with respect to allow_maximum_power() or allocate_power()
> >>> does not matter.
> >>>
> >>> Accordingly, make power_allocator_manage() update that field right
> >>> before returning, which allows the current value of it to be passed
> >>> directly to allow_maximum_power() without using the additional update
> >>> variable that can be dropped.
> >>>
> >>> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> >>> ---
> >>
> >> The step_wise and the power allocator are changing the tz->passive
> >> values, so telling the core to start and stop the passive mitigation timer.
> >>
> >> It looks strange that a plugin controls the core internal and not the
> >> opposite.
> >>
> >> I'm wondering if it would not make sense to have the following ops:
> >>
> >>          .start
> >>          .stop
> >>
> >> .start is called when the first trip point is crossed the way up
> >> .stop is called when the first trip point is crossed the way down
> >>
> >>    - The core is responsible to start and stop the passive mitigation timer.
> >>
> >>    - the governors do no longer us tz->passive
> >>
> >> The reset of the governor can happen at start or stop, as well as the
> >> device cooling states.
> >
> > I have a patch that simply increments tz->passive when a passive trip
> > point is passed on the way up and decrements it when a passive trip
> > point is crossed on the way down.  It appears to work reasonably well.
>
> Does it make the governors getting ride of it ? Or at least not changing
> its value ?

Not yet, but I'm going to update it this way.  The governors should
not mess up with tz->passive IMV.