linux-kernel - Re: [RFC 3/4] ARM: topology: Update cpu

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Date:	Wed, 13 Jun 2012 10:59:25 +0200
From:	Jean Pihet <jean.pihet@...oldbits.com>
To:	Vincent Guittot <vincent.guittot@...aro.org>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linaro-dev@...ts.linaro.org, devicetree-discuss@...ts.ozlabs.org,
	linux@....linux.org.uk, peterz@...radead.org,
	grant.likely@...retlab.ca, rob.herring@...xeda.com
Subject: Re: [RFC 3/4] ARM: topology: Update cpu_power according to DT information

Vincent,

On Tue, Jun 12, 2012 at 2:02 PM, Vincent Guittot
<vincent.guittot@...aro.org> wrote:
> Use cpu compatibility field and clock-frequency field of DT to
> estimate the capacity of each core of the system
>
> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
> ---
>  arch/arm/kernel/topology.c |  122 ++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 122 insertions(+)
>
> diff --git a/arch/arm/kernel/topology.c b/arch/arm/kernel/topology.c
> index 2f85a64..0c2aee4 100644
> --- a/arch/arm/kernel/topology.c
> +++ b/arch/arm/kernel/topology.c
> @@ -17,6 +17,7 @@
>  #include <linux/percpu.h>
>  #include <linux/node.h>
>  #include <linux/nodemask.h>
> +#include <linux/of.h>
>  #include <linux/sched.h>
>
>  #include <asm/cputype.h>
> @@ -47,6 +48,122 @@ void set_power_scale(unsigned int cpu, unsigned long power)
>        per_cpu(cpu_scale, cpu) = power;
>  }
>
> +#ifdef CONFIG_OF
> +struct cpu_efficiency {
> +       const char *compatible;
> +       unsigned long efficiency;
> +};
> +
> +/*
> + * Table of relative efficiency of each processors
> + * The efficiency value must fit in 20bit. The final
> + * cpu_scale value must be in the range [1:2048[.
Typo here.

> + * Processors that are not defined in the table,
> + * use the default SCHED_POWER_SCALE value for cpu_scale.
> + */
> +struct cpu_efficiency table_efficiency[] = {
> +       {"arm,cortex-a15", 3891},
> +       {"arm,cortex-a7",  2048},
How are those results measured or computed? Is this purely related to
the number crunching performance?

Also more generally what if the cores frequencies are changing?

Regards,
Jean
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