Re: [RFCv3 PATCH 14/48] arm: Frequency invariant scheduler load-tracking support

[Peter Zijlstra]

On Wed, Feb 04, 2015 at 06:30:51PM +0000, Morten Rasmussen wrote:
> +/* cpufreq callback function setting current cpu frequency */
> +void arch_scale_set_curr_freq(int cpu, unsigned long freq)
> +{
> +	atomic_long_set(&per_cpu(cpu_curr_freq, cpu), freq);
> +}
> +
> +/* cpufreq callback function setting max cpu frequency */
> +void arch_scale_set_max_freq(int cpu, unsigned long freq)
> +{
> +	atomic_long_set(&per_cpu(cpu_max_freq, cpu), freq);
> +}
> +
> +unsigned long arch_scale_freq_capacity(struct sched_domain *sd, int cpu)
> +{
> +	unsigned long curr = atomic_long_read(&per_cpu(cpu_curr_freq, cpu));
> +	unsigned long max = atomic_long_read(&per_cpu(cpu_max_freq, cpu));
> +
> +	if (!curr || !max)
> +		return SCHED_CAPACITY_SCALE;
> +
> +	return (curr * SCHED_CAPACITY_SCALE) / max;
> +}

so I've no idea how many cycles an (integer) division takes on ARM; but
doesn't it make sense to do this division (once) in
arch_scale_set_curr_freq() instead of every time we need the result?
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