linux-kernel - Re: [RFC][PATCH 3/5] thermal: Add support for setting notification thresholds

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Message-ID: <CAHLCerOsZrrZYcRLH+iZFT9FPL8zfmy2Y-Py6f61YXUrMrkcbg@mail.gmail.com>
Date:   Thu, 21 May 2020 10:41:04 +0530
From:   Amit Kucheria <amit.kucheria@...durent.com>
To:     Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Cc:     Daniel Lezcano <daniel.lezcano@...aro.org>,
        Zhang Rui <rui.zhang@...el.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux PM list <linux-pm@...r.kernel.org>
Subject: Re: [RFC][PATCH 3/5] thermal: Add support for setting notification thresholds

Hi Srinivas,

On Wed, May 20, 2020 at 11:46 PM Srinivas Pandruvada
<srinivas.pandruvada@...ux.intel.com> wrote:
>
> On Wed, 2020-05-20 at 09:58 +0530, Amit Kucheria wrote:
> > On Tue, May 19, 2020 at 5:10 AM Srinivas Pandruvada
> > <srinivas.pandruvada@...ux.intel.com> wrote:
> > > On Mon, 2020-05-18 at 18:37 +0200, Daniel Lezcano wrote:
> > > > On 04/05/2020 20:16, Srinivas Pandruvada wrote:
> > > > > Add new attributes in thermal syfs when a thermal drivers
> > > > > provides
> > > > > callbacks for them and CONFIG_THERMAL_USER_EVENT_INTERFACE is
> > > > > defined.
> > > > >
> > > > > These attribute allow user space to stop polling for
> > > > > temperature.
> > > > >
> > > > > These attributes are:
> > > > > - temp_thres_low: Specify a notification temperature for a low
> > > > > temperature threshold event.
> > > > > temp_thres_high: Specify a notification temperature for a high
> > > > > temperature threshold event.
> > > > > temp_thres_hyst: Specify a change in temperature to send
> > > > > notification
> > > > > again.
> > > > >
> > > > > This is implemented by adding additional sysfs attribute group.
> > > > > The
> > > > > changes in this patch are trivial to add new attributes in
> > > > > thermal
> > > > > sysfs as done for other attributes.
> > > >
> > > > Isn't it duplicate with the trip point?
> > > A trip point is where an in-kernel governor takes some action. This
> > > is
> > > not same as a notification temperature. For example at trip point
> > > configured by ACPI at 85C, the thermal governor may start
> > > aggressive
> > > throttling.
> > > But a user space can set a notification threshold at 80C and start
> > > some
> > > active controls like activate some fan to reduce the impact of
> > > passive
> > > control on performance.
> >
> > Then what is the use of thermal trip type "ACTIVE" ?
> This is an example.
> The defaults are set by the OEMs via ACPI. User can't modify that if
> they want to optimize for their usage on Linux. There are fan control
> daemon's which user use on top.

-ENOPARSE. Are you saying users "can" modify these?

In any case, how is what you described earlier not possible with an
ACTIVE trip point directly wired to the fan as a cooling device or
with a HOT trip point that causes the platform driver to send
notification to userspace where a fan control daemon can do what it
needs to?

Basically, I think the issue of polling is orthogonal to the
introduction of the new attributes introduced in this patch and I
don't understand the reason for these attributes from your commit
description.

> > > We need a way to distinguish between temperature notification
> > > threshold
> > > and actual trip point. Changing a trip point means that user wants
> > > kernel to throttle at temperature.
>