[RFC PATCH] thermal: power_allocator: Ignore cutoff when integral is less than zero

[Xuewen Yan]

From: Jeson Gao <jeson.gao@xxxxxxxxxx>

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@xxxxxxxxxx>
Signed-off-by: Di Shen <di.shen@xxxxxxxxxx>
Signed-off-by: Jeson Gao <jeson.gao@xxxxxxxxxx>
Signed-off-by: Xuewen Yan <xuewen.yan@xxxxxxxxxx>
---
 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