linux-kernel - Re: [PATCH v2 4/7] thermal: introduce the Power Allocator governor

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Date:	Thu, 26 Feb 2015 16:36:16 -0400
From:	Eduardo Valentin <edubezval@...il.com>
To:	Javi Merino <javi.merino@....com>
Cc:	rui.zhang@...el.com, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, punit.agrawal@....com,
	broonie@...nel.org, tixy@...aro.org
Subject: Re: [PATCH v2 4/7] thermal: introduce the Power Allocator governor

Javi,

Replying in v2.

On Thu, Feb 26, 2015 at 07:00:30PM +0000, Javi Merino wrote:

<big cut>

> +
> +/**
> + * divvy_up_power() - divvy the allocated power between the actors
> + * @req_power:	each actor's requested power
> + * @max_power:	each actor's maximum available power
> + * @num_actors:	size of the @req_power, @max_power and @granted_power's array
> + * @total_req_power: sum of @req_power
> + * @power_range:	total allocated power
> + * @granted_power:	output array: each actor's granted power
> + *
> + * This function divides the total allocated power (@power_range)
> + * fairly between the actors.  It first tries to give each actor a
> + * share of the @power_range according to how much power it requested
> + * compared to the rest of the actors.  For example, if only one actor
> + * requests power, then it receives all the @power_range.  If
> + * three actors each requests 1mW, each receives a third of the
> + * @power_range.
> + *
> + * If any actor received more than their maximum power, then that
> + * surplus is re-divvied among the actors based on how far they are
> + * from their respective maximums.
> + *
> + * Granted power for each actor is written to @granted_power, which
> + * should've been allocated by the calling function.
> + */
> +static void divvy_up_power(u32 *req_power, u32 *max_power, int num_actors,
> +			   u32 total_req_power, u32 power_range,
> +			   u32 *granted_power)
> +{
> +	u32 extra_power, capped_extra_power, extra_actor_power[num_actors];

Just now I noticed this variable-size array. I know the number of actors
are constant, and in average it should be less than 10 in magnitude, but
I don't believe variable-sized arrays are a good practice in kernel.

Even though I don't see this one as a treat, can we avoid it?
Sparse error:

drivers/thermal/power_allocator.c:172:64: error: bad constant expression


BR,

Eduardo Valentin

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