Re: [PATCH V2] thermal/drivers/step_wise: Fix temperature regulation misbehavior

From: Keerthy
Date: Fri Sep 08 2017 - 05:49:43 EST



On Friday 08 September 2017 02:35 PM, Daniel Lezcano wrote:
> There is a particular situation when the cooling device is cpufreq and the heat
> dissipation is not efficient enough where the temperature increases little by
> little until reaching the critical threshold and leading to a SoC reset.
>
> The behavior is reproducible on a hikey6220 with bad heat dissipation (eg.
> stacked with other boards).
>
> Running a simple C program doing while(1); for each CPU of the SoC makes the
> temperature to reach the passive regulation trip point and ends up to the
> maximum allowed temperature followed by a reset.
>
> This issue has been also reported by running the libhugetlbfs test suite.
>
> What is observed is a ping pong between two cpu frequencies, 1.2GHz and 900MHz
> while the temperature continues to grow.
>
> It appears the step wise governor calls get_target_state() the first time with
> the throttle set to true and the trend to 'raising'. The code selects logically
> the next state, so the cpu frequency decreases from 1.2GHz to 900MHz, so far so
> good. The temperature decreases immediately but still stays greater than the
> trip point, then get_target_state() is called again, this time with the
> throttle set to true *and* the trend to 'dropping'. From there the algorithm
> assumes we have to step down the state and the cpu frequency jumps back to
> 1.2GHz. But the temperature is still higher than the trip point, so
> get_target_state() is called with throttle=1 and trend='raising' again, we jump
> to 900MHz, then get_target_state() is called with throttle=1 and
> trend='dropping', we jump to 1.2GHz, etc ... but the temperature does not
> stabilizes and continues to increase.
>
> [ 237.922654] thermal thermal_zone0: Trip0[type=1,temp=65000]:trend=1,throttle=1
> [ 237.922678] thermal thermal_zone0: Trip1[type=1,temp=75000]:trend=1,throttle=1
> [ 237.922690] thermal cooling_device0: cur_state=0
> [ 237.922701] thermal cooling_device0: old_target=0, target=1
> [ 238.026656] thermal thermal_zone0: Trip0[type=1,temp=65000]:trend=2,throttle=1
> [ 238.026680] thermal thermal_zone0: Trip1[type=1,temp=75000]:trend=2,throttle=1
> [ 238.026694] thermal cooling_device0: cur_state=1
> [ 238.026707] thermal cooling_device0: old_target=1, target=0
> [ 238.134647] thermal thermal_zone0: Trip0[type=1,temp=65000]:trend=1,throttle=1
> [ 238.134667] thermal thermal_zone0: Trip1[type=1,temp=75000]:trend=1,throttle=1
> [ 238.134679] thermal cooling_device0: cur_state=0
> [ 238.134690] thermal cooling_device0: old_target=0, target=1
>
> In this situation the temperature continues to increase while the trend is
> oscillating between 'dropping' and 'raising'. We need to keep the current state
> untouched if the throttle is set, so the temperature can decrease or a higher
> state could be selected, thus prevening this oscillation.
>
> Keeping the next_target untouched when 'throttle' is true at 'dropping' time
> fixes the issue.
>
> The following traces show the governor does not change the next state if
> trend==2 (dropping) and throttle==1.
>
> [ 2306.127987] thermal thermal_zone0: Trip0[type=1,temp=65000]:trend=1,throttle=1
> [ 2306.128009] thermal thermal_zone0: Trip1[type=1,temp=75000]:trend=1,throttle=1
> [ 2306.128021] thermal cooling_device0: cur_state=0
> [ 2306.128031] thermal cooling_device0: old_target=0, target=1
> [ 2306.231991] thermal thermal_zone0: Trip0[type=1,temp=65000]:trend=2,throttle=1
> [ 2306.232016] thermal thermal_zone0: Trip1[type=1,temp=75000]:trend=2,throttle=1
> [ 2306.232030] thermal cooling_device0: cur_state=1
> [ 2306.232042] thermal cooling_device0: old_target=1, target=1
> [ 2306.335982] thermal thermal_zone0: Trip0[type=1,temp=65000]:trend=0,throttle=1
> [ 2306.336006] thermal thermal_zone0: Trip1[type=1,temp=75000]:trend=0,throttle=1
> [ 2306.336021] thermal cooling_device0: cur_state=1
> [ 2306.336034] thermal cooling_device0: old_target=1, target=1
> [ 2306.439984] thermal thermal_zone0: Trip0[type=1,temp=65000]:trend=2,throttle=1
> [ 2306.440008] thermal thermal_zone0: Trip1[type=1,temp=75000]:trend=2,throttle=0
> [ 2306.440022] thermal cooling_device0: cur_state=1
> [ 2306.440034] thermal cooling_device0: old_target=1, target=0
>
> [ ... ]
>
> After a while, if the temperature continues to increase, the next state becomes
> 2 which is 720MHz on the hikey. That results in the temperature stabilizing
> around the trip point.
>
> [ 2455.831982] thermal thermal_zone0: Trip0[type=1,temp=65000]:trend=1,throttle=1
> [ 2455.832006] thermal thermal_zone0: Trip1[type=1,temp=75000]:trend=1,throttle=0
> [ 2455.832019] thermal cooling_device0: cur_state=1
> [ 2455.832032] thermal cooling_device0: old_target=1, target=1
> [ 2455.935985] thermal thermal_zone0: Trip0[type=1,temp=65000]:trend=0,throttle=1
> [ 2455.936013] thermal thermal_zone0: Trip1[type=1,temp=75000]:trend=0,throttle=0
> [ 2455.936027] thermal cooling_device0: cur_state=1
> [ 2455.936040] thermal cooling_device0: old_target=1, target=1
> [ 2456.043984] thermal thermal_zone0: Trip0[type=1,temp=65000]:trend=0,throttle=1
> [ 2456.044009] thermal thermal_zone0: Trip1[type=1,temp=75000]:trend=0,throttle=0
> [ 2456.044023] thermal cooling_device0: cur_state=1
> [ 2456.044036] thermal cooling_device0: old_target=1, target=1
> [ 2456.148001] thermal thermal_zone0: Trip0[type=1,temp=65000]:trend=1,throttle=1
> [ 2456.148028] thermal thermal_zone0: Trip1[type=1,temp=75000]:trend=1,throttle=1
> [ 2456.148042] thermal cooling_device0: cur_state=1
> [ 2456.148055] thermal cooling_device0: old_target=1, target=2
> [ 2456.252009] thermal thermal_zone0: Trip0[type=1,temp=65000]:trend=2,throttle=1
> [ 2456.252041] thermal thermal_zone0: Trip1[type=1,temp=75000]:trend=2,throttle=0
> [ 2456.252058] thermal cooling_device0: cur_state=2
> [ 2456.252075] thermal cooling_device0: old_target=2, target=1
>
> IOW, this change is needed to keep the state for a cooling device if the
> temperature trend is oscillating while the temperature increases slightly.
>
> Without this change, the situation above leads to a catastrophic crash by a
> hardware reset on hikey.

Daniel,

By design this governor is throttling and un-throttling based on the
computed trend.

Why not add an intermediate trip point with the highest cooling enabled.
Say High alert trip point that allows only the lowest OPP for cpufreq to
operate.

For example: alert trip is at 100C (where cpufreq cooling kicks in)
critical trip is at 125C(shutdown temperature).

We have Something like below @110C which allows only the lowest
frequency or lowest 2 frequencies based on experimentation:

+&cpu_trips {
+ cpu_high_alert: cpu_high_alert {
+ temperature = <110000>; /* millicelsius */
+ hysteresis = <2000>; /* millicelsius */
+ type = "passive";
+ };
+};
+
+&cpu_cooling_maps {
+ map1: map1 {
+ trip = <&cpu_high_alert>;
+ cooling-device =
+ <&cpu0 2 THERMAL_NO_LIMIT>;
+ };
+};
+

I have seen this problem myself on dra7 platforms. The above will cool
the device post 110C by keeping the cpu frequency at the lowest or lower
values. That way when you are in between 100 - 110C you can still get
highest performance depending on the trend computed and post 110C.

My 2 cents on this.

Regards,
Keerthy
>
> Signed-off-by: Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>
> ---
> drivers/thermal/step_wise.c | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/thermal/step_wise.c b/drivers/thermal/step_wise.c
> index bd2f133..703bd0d 100644
> --- a/drivers/thermal/step_wise.c
> +++ b/drivers/thermal/step_wise.c
> @@ -95,9 +95,11 @@ static unsigned long get_target_state(struct thermal_instance *instance,
> if (!throttle)
> next_target = THERMAL_NO_TARGET;
> } else {
> - next_target = cur_state - 1;
> - if (next_target > instance->upper)
> - next_target = instance->upper;
> + if (!throttle) {
> + next_target = cur_state - 1;
> + if (next_target > instance->upper)
> + next_target = instance->upper;
> + }
> }
> break;
> case THERMAL_TREND_DROP_FULL:
>