ACK: [PATCH 3/4] cpu: cpufreq: sort frequencies using almost equal comparison (LP: #1322531)

[Alex Hung]

On 05/23/2014 08:42 PM, Colin King wrote:
> From: Colin Ian King <colin.king at canonical.com>
>
> Some _PSS states have top turbo frequencies that are set at the same level
> or nearly the same level as the next fast _PSS non-turbo level.  Sometimes
> this confuses the qsort, so make the qsort compare function also sub-sort
>
> Signed-off-by: Colin Ian King <colin.king at canonical.com>
> ---
>   src/cpu/cpufreq/cpufreq.c | 39 ++++++++++++++++++++++++++++++++++++++-
>   1 file changed, 38 insertions(+), 1 deletion(-)
>
> diff --git a/src/cpu/cpufreq/cpufreq.c b/src/cpu/cpufreq/cpufreq.c
> index 91e44f9..22e16ef 100644
> --- a/src/cpu/cpufreq/cpufreq.c
> +++ b/src/cpu/cpufreq/cpufreq.c
> @@ -59,6 +59,34 @@ static int num_cpus;
>   #define GET_PERFORMANCE_MIN (1)
>   #define GET_PERFORMANCE_AVG (2)
>
> +#define MAX_ABSOLUTE_ERROR	20.0		/* In Hz */
> +#define MAX_RELATIVE_ERROR	0.0025		/* as fraction */
> +
> +/*
> + *  hz_almost_equal()
> + *	used to compare CPU _PSS levels, are they almost
> + *	equal?  E.g. within MAX_ABSOLUTE_ERROR Hz difference
> + *	between each other, or a relative difference of
> + *	MAX_RELATIVE_ERROR.  If they are, then they are deemed
> + *	almost equal.
> + */
> +static int hz_almost_equal(const uint64_t a, const uint64_t b)
> +{
> +	double da = (double)a, db = (double)b;
> +	double relative_error, abs_diff = fabs(da - db);
> +
> +	if (a == b)
> +		return true;
> +	if (abs_diff < MAX_ABSOLUTE_ERROR)
> +		return true;
> +	if (db > da)
> +		relative_error = abs_diff / db;
> +	else
> +		relative_error = abs_diff / da;
> +
> +	return relative_error <= MAX_RELATIVE_ERROR;
> +}
> +
>   static inline void cpu_mkpath(
>   	char *const path,
>   	const int len,
> @@ -224,7 +252,16 @@ static int cpu_freq_compare(const void *v1, const void *v2)
>   	const fwts_cpu_freq *cpu_freq1 = (fwts_cpu_freq *)v1;
>   	const fwts_cpu_freq *cpu_freq2 = (fwts_cpu_freq *)v2;
>
> -	return cpu_freq1->Hz - cpu_freq2->Hz;
> +	/*
> +	 * Some _PSS states can be the same or very nearly
> +	 * the same when Turbo mode is available,
> +	 * so if they are we also differentiate the two by
> +	 * the speed to get a fully sorted ordering
> +	 */
> +	if (hz_almost_equal(cpu_freq1->Hz, cpu_freq2->Hz))
> +		return cpu_freq1->speed - cpu_freq2->speed;
> +	else
> +		return cpu_freq1->Hz - cpu_freq2->Hz;
>   }
>
>   static int read_freqs_available(const int cpu, fwts_cpu_freq *freqs)
>

Acked-by: Alex Hung <alex.hung at canonical.com>