RE: [RFC PATCH 3/3] arm64: dts: renesas: r9a09g047: Add thermal hotplug trip point

[John Madieu <john.madieu.xa@bp.renesas.com>]

Hi Christian,

Thanks for reviewing.

> -----Original Message-----
> From: Christian Loehle <christian.loehle@arm.com>
> Sent: Tuesday, March 11, 2025 11:53 AM
> To: John Madieu <john.madieu.xa@bp.renesas.com>; geert+renesas@glider.be;
> niklas.soderlund+renesas@ragnatech.se; conor+dt@kernel.org;
> krzk+dt@kernel.org; robh@kernel.org; rafael@kernel.org;
> daniel.lezcano@linaro.org
> Cc: magnus.damm@gmail.com; Claudiu Beznea
> <claudiu.beznea.uj@bp.renesas.com>; devicetree@vger.kernel.org;
> john.madieu@gmail.com; rui.zhang@intel.com; linux-kernel@vger.kernel.org;
> linux-renesas-soc@vger.kernel.org; Biju Das <biju.das.jz@bp.renesas.com>;
> linux-pm@vger.kernel.org
> Subject: Re: [RFC PATCH 3/3] arm64: dts: renesas: r9a09g047: Add thermal
> hotplug trip point
> 
> On 3/9/25 12:13, John Madieu wrote:
> > Add CPU hotplug trip point to shutdown CPU1 and CPU2 when exceeding
> 110°C.
> >
> > Signed-off-by: John Madieu <john.madieu.xa@bp.renesas.com>
> > ---
> >  arch/arm64/boot/dts/renesas/r9a09g047.dtsi | 13 +++++++++++++
> >  1 file changed, 13 insertions(+)
> >
> > diff --git a/arch/arm64/boot/dts/renesas/r9a09g047.dtsi
> > b/arch/arm64/boot/dts/renesas/r9a09g047.dtsi
> > index 93b57d7ad7b9..06bd394582e2 100644
> > --- a/arch/arm64/boot/dts/renesas/r9a09g047.dtsi
> > +++ b/arch/arm64/boot/dts/renesas/r9a09g047.dtsi
> > @@ -533,6 +533,13 @@ map0 {
> >  							 <&cpu2 0 3>, <&cpu3 0 3>;
> >  					contribution = <1024>;
> >  				};
> > +
> > +				map1 {
> > +					trip = <&trip_emergency>;
> > +					cooling-device = <&cpu1 0 1>, <&cpu2 0 1>;
> > +					contribution = <1024>;
> > +				};
> > +
> >  			};
> >
> >  			trips {
> > @@ -542,6 +549,12 @@ target: trip-point {
> >  					type = "passive";
> >  				};
> >
> > +				trip_emergency: emergency {
> > +					temperature = <110000>;
> > +					hysteresis = <1000>;
> > +					type = "plug";
> > +				};
> > +
> >  				sensor_crit: sensor-crit {
> >  					temperature = <120000>;
> >  					hysteresis = <1000>;
> 
> 
> Are there no other cooling methods?
> How does it compare to idle inject?
> 
> Furthermore, couldn't the offlining of some CPUs lead to the rest being
> operated at much higher OPPs therefore the overall power increase, too?
> (Without having looked at if this is a possibility for this particular
> SoC.)
> Some numbers would be helpful IMO.

To clarify this, I tested with CPUFreq cooling, along with performance
Governor, with "plug" threshold higher than "passive" one. When passive
trip is crossed, we observe proper CPUs throttling, and when "plug" trip
is crossed, we observe target CPUs being put offline, while throttling
remains.

When "plug" targeted CPUs come back online, throttling is still operational.

Once I get comparison results with CPU idle cooling, I'll keep you posted.

Regards,
John.