linux-kernel - Re: [PATCH] thermal: gov_power_allocator: Fix incorrect calculation in divvy_up

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Message-ID: <CAJZ5v0jSh=aOfP7BKTCSxnPGy-XKJKcHNw8bN5PXPH0LA0tAGg@mail.gmail.com>
Date: Thu, 20 Feb 2025 20:45:01 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Yu-Che Cheng <giver@...omium.org>, Lukasz Luba <lukasz.luba@....com>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, Daniel Lezcano <daniel.lezcano@...aro.org>, 
	Zhang Rui <rui.zhang@...el.com>, "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>, 
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Chen-Yu Tsai <wenst@...omium.org>
Subject: Re: [PATCH] thermal: gov_power_allocator: Fix incorrect calculation
 in divvy_up_power

On Wed, Feb 19, 2025 at 8:07 AM Yu-Che Cheng <giver@...omium.org> wrote:
>
> divvy_up_power should use weighted_req_power instead of req_power to
> calculate the granted_power. Otherwise, the granted_power may be
> unexpected as the denominator total_req_power is weighted sum.

Yes, this is what's happening, to my eyes.

> This is a mistake during the previous refactor.
>
> Replace the req_power with weighted_req_power in divvy_up_power
> calculation.
>
> Fixes: 912e97c67cc3 ("thermal: gov_power_allocator: Move memory allocation out of throttle()")
> Signed-off-by: Yu-Che Cheng <giver@...omium.org>
> ---
>  drivers/thermal/gov_power_allocator.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/thermal/gov_power_allocator.c b/drivers/thermal/gov_power_allocator.c
> index 3b644de3292e..3b626db55b2b 100644
> --- a/drivers/thermal/gov_power_allocator.c
> +++ b/drivers/thermal/gov_power_allocator.c
> @@ -370,7 +370,7 @@ static void divvy_up_power(struct power_actor *power, int num_actors,
>
>         for (i = 0; i < num_actors; i++) {
>                 struct power_actor *pa = &power[i];
> -               u64 req_range = (u64)pa->req_power * power_range;
> +               u64 req_range = (u64)pa->weighted_req_power * power_range;
>
>                 pa->granted_power = DIV_ROUND_CLOSEST_ULL(req_range,
>                                                           total_req_power);
>
> ---

And the fix looks good to me.

Lukasz, any concerns?