Messages in this thread | | | Subject | Re: [PATCH] thermal: power_allocate: add upper and lower limits | From | Lukasz Luba <> | Date | Wed, 29 Apr 2020 21:24:43 +0100 |
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On 4/29/20 11:39 AM, Michael Kao wrote: > On Fri, 2020-04-24 at 10:22 +0100, Lukasz Luba wrote: >> Hi Michael, >> >> On 4/24/20 8:16 AM, Michael Kao wrote: >>> The upper and lower limits of thermal throttle state in the >>> device tree do not apply to the power_allocate governor. >>> Add the upper and lower limits to the power_allocate governor. >>> >>> Signed-off-by: Michael Kao <michael.kao@mediatek.com> >>> --- >>> drivers/thermal/thermal_core.c | 2 +- >>> 1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/drivers/thermal/thermal_core.c b/drivers/thermal/thermal_core.c >>> index 9a321dc548c8..f6feed2265bd 100644 >>> --- a/drivers/thermal/thermal_core.c >>> +++ b/drivers/thermal/thermal_core.c >>> @@ -598,7 +598,7 @@ int power_actor_set_power(struct thermal_cooling_device *cdev, >>> if (ret) >>> return ret; >>> >>> - instance->target = state; >>> + instance->target = clamp_val(state, instance->lower, instance->upper); >>> mutex_lock(&cdev->lock); >>> cdev->updated = false; >>> mutex_unlock(&cdev->lock); >>> >> >> Thank you for the patch and having to look at it. I have some concerns >> with this approach. Let's analyze it further. >> >> In default the cooling devices in the thermal zone which is used by IPA >> do not have this 'lower' and 'upper' limits. They are set to >> THERMAL_NO_LIMIT in DT to give full control to IPA over the states. >> >> This the function 'power_actor_set_power' actually translates granted >> power to the state that device will run for the next period. >> The IPA algorithm has already split the power budget. >> Now what happen when the 'lower' value will change the state to a state >> which consumes more power than was calculated in the IPA alg... It will >> became unstable. >> >> I would rather see a change which uses these 'lower' and 'upper' limits >> before the IPA do the calculation of the power budget. But this wasn't >> a requirement and we assumed that IPA has full control over the cooling >> device (which I described above with this DT THERMAL_NO_LIMIT). >> >> Is there a problem with your platform that it has to provide some >> minimal performance, so you tried to introduce this clamping? >> >> Regards, >> Lukasz > > > Hi Lukasz, > > I refer to the documentation settings of the thermal device tree > (Documentation / devicetree / bindings / thermal / thermal.txt). > > It shows that cooling-device is a mandatory property, so max/min cooling > state should be able to support in framework point of view. > Otherwise, the limitation should be added in binding document. > > Different hardware mechanisms have different heat dissipation > capabilities. > Limiting the input heat source can slow down the heat accumulation and > temperature burst. > We want to reduce the accumulation of heat at high temperature by > limiting the minimum gear of thermal throttle.
I agree that these 'lower' and 'upper' limits shouldn't be just ignored as is currently. This patch clamps the value at late stage, though.
Let me have a look how it could be taken into account in the early stage, before the power calculation and split are done. Maybe there is a clean way to inject this.
Regards, Lukasz
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