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

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Date:   Wed, 20 May 2020 11:16:46 -0700
From:   Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
To:     Amit Kucheria <amit.kucheria@...durent.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 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.

Thanks,
Srinivas

> 
> > 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.