linux-kernel - Re: [RFC PATCH] thermal: power_allocator: Ignore cutoff when integral is less than zero

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Message-ID: <CAB8ipk93vxpuSF3msuryedefJ8v_4ZMrk56MFaGp8+Mh-EqnSA@mail.gmail.com>
Date: Mon, 26 Jan 2026 11:24:26 +0800
From: Xuewen Yan <xuewen.yan94@...il.com>
To: Xuewen Yan <xuewen.yan@...soc.com>
Cc: lukasz.luba@....com, rafael@...nel.org, daniel.lezcano@...aro.org, 
	rui.zhang@...el.com, linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	ke.wang@...soc.com, jeson.gao@...soc.com, di.shen@...soc.com
Subject: Re: [RFC PATCH] thermal: power_allocator: Ignore cutoff when integral
 is less than zero

Hi lukasz,

Do you have any comments on this patch?

Thanks!

On Mon, Jan 19, 2026 at 10:00 AM Xuewen Yan <xuewen.yan@...soc.com> wrote:
>
> From: Jeson Gao <jeson.gao@...soc.com>
>
> The cutoff means threshold below which the error is no longer accumulated.
> However, in some scenarios, this may cause performance degradation.
>
> For example:
> the control-temp is 85, the cutoff is 0 or other small value:
>
> If the current temperature frequently exceeds the set temperature,
> the negative integral will continuously accumulate.
> Over an extended period, this will result in a significantly
> large negative integral value, the positive integral can’t build up
> because of the cutoff. This makes the power_range very low,
> even if the temperature is already under the control target.
>
> So, if the err_integral is negative, ignore the cutoff to force
> add the positive integral.
>
> Co-developed-by: Di Shen <di.shen@...soc.com>
> Signed-off-by: Di Shen <di.shen@...soc.com>
> Signed-off-by: Jeson Gao <jeson.gao@...soc.com>
> Signed-off-by: Xuewen Yan <xuewen.yan@...soc.com>
> ---
>  drivers/thermal/gov_power_allocator.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/thermal/gov_power_allocator.c b/drivers/thermal/gov_power_allocator.c
> index 0d9f636c80f4..404ae1d75612 100644
> --- a/drivers/thermal/gov_power_allocator.c
> +++ b/drivers/thermal/gov_power_allocator.c
> @@ -263,7 +263,8 @@ static u32 pid_controller(struct thermal_zone_device *tz,
>          */
>         i = mul_frac(tz->tzp->k_i, params->err_integral);
>
> -       if (err < int_to_frac(tz->tzp->integral_cutoff)) {
> +       if (err < int_to_frac(tz->tzp->integral_cutoff) ||
> +           (err > 0 && params->err_integral < 0)) {
>                 s64 i_next = i + mul_frac(tz->tzp->k_i, err);
>
>                 if (abs(i_next) < max_power_frac) {
> --
> 2.25.1
>