• Daniel Lezcano's avatar
    thermal/drivers/step_wise: Fix temperature regulation misbehavior · 07209fcf
    Daniel Lezcano authored
    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.
    Signed-off-by: default avatarDaniel Lezcano <daniel.lezcano@linaro.org>
    Cc: Keerthy <j-keerthy@ti.com>
    Cc: John Stultz <john.stultz@linaro.org>
    Cc: Leo Yan <leo.yan@linaro.org>
    Tested-by: default avatarKeerthy <j-keerthy@ti.com>
    Reviewed-by: default avatarKeerthy <j-keerthy@ti.com>
    Signed-off-by: default avatarEduardo Valentin <edubezval@gmail.com>
step_wise.c 6.7 KB