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

[Christian Loehle <christian.loehle@arm.com>]

On 3/11/25 11:57, John Madieu wrote:
> 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.
> 

Thanks John!
Might make sense to also try this with schedutil, because my argument doesn't
hold with performance governor.
As long as we also have throttling that's not a concern anyway.