Re: [PATCH V3] thermal/drivers/step_wise: Fix temperature regulation misbehavior

[Keerthy]

On Friday 08 September 2017 07:42 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 preventing 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. This issue has been reported to happen on an OMAP
> dra7xx also.

Tested on am57xx-evm and saw that cooling level was not reduced even
when temperatures dropped(Negative trend) when the current temperature
was above trip point.

The cooling level was only reduced when the current temperature fell
below the trip point.

Tested-by: Keerthy <j-keerthy@xxxxxx>
Reviewed-by: Keerthy <j-keerthy@xxxxxx>

> 
> Signed-off-by: Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>
> Cc: Keerthy <j-keerthy@xxxxxx>
> Cc: John Stultz <john.stultz@xxxxxxxxxx>
> Cc: Leo Yan <leo.yan@xxxxxxxxxx>
> ---
>  drivers/thermal/step_wise.c | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/thermal/step_wise.c b/drivers/thermal/step_wise.c
> index be95826..ee047ca 100644
> --- a/drivers/thermal/step_wise.c
> +++ b/drivers/thermal/step_wise.c
> @@ -31,8 +31,7 @@
>   * If the temperature is higher than a trip point,
>   *    a. if the trend is THERMAL_TREND_RAISING, use higher cooling
>   *       state for this trip point
> - *    b. if the trend is THERMAL_TREND_DROPPING, use lower cooling
> - *       state for this trip point
> + *    b. if the trend is THERMAL_TREND_DROPPING, do nothing
>   *    c. if the trend is THERMAL_TREND_RAISE_FULL, use upper limit
>   *       for this trip point
>   *    d. if the trend is THERMAL_TREND_DROP_FULL, use lower limit
> @@ -94,9 +93,11 @@ 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:
>