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

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Message-ID: <CAHLCerMfnHPuJnj6G4EvRPvODf1_Se4xM-OobA1o7eao5eetzg@mail.gmail.com>
Date:   Wed, 20 May 2020 09:58:18 +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

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" ?

> 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.