Re: PATCH] ftrace: Add a C/P state tracer to help power optimization

[Ingo Molnar <mingo@elte.hu>]

* Arjan van de Ven <arjan@infradead.org> wrote:

> From: Arjan van de Ven <arjan@linux.intel.com>
> Date: Fri, 3 Oct 2008 10:18:21 -0700
> Subject: [PATCH] ftrace: Add a C/P state tracer to help power optimization
> 
> This patch adds a C/P-state ftrace plugin that will generate
> detailed statistics about the C/P-states that are being used,
> so that we can look at detailed decisions that the C/P-state
> code is making, rather than the too high level "average"
> that we have today.

nice! No fundamental objections - Len, do you concur? We could carry 
this in the ftrace tree, the impact on the rest of the kernel is 
minimal.

A few minor nits:

>  static void poll_idle(void)
>  {
> +	struct power_trace it;
> +	trace_power_start(&it, POWER_CSTATE, 0);

please put a newline after variable definitions.

> --- a/include/linux/ftrace.h
> +++ b/include/linux/ftrace.h
> @@ -232,6 +232,32 @@ static inline void start_boot_trace(void) { }
>  static inline void stop_boot_trace(void) { }
>  #endif
>  
> +#define POWER_NONE 0
> +#define POWER_CSTATE 1
> +#define POWER_PSTATE 2
> +struct power_trace {

the defines should be an enum and please put a newline after the enum 
definition.

> +#ifdef CONFIG_POWER_TRACER
> +	ktime_t			stamp;
> +	ktime_t			end;
> +	int			type;
> +	int			state;
> +#endif
> +};

> index 396aea1..1f797bd 100644
> --- a/kernel/trace/Kconfig
> +++ b/kernel/trace/Kconfig
> @@ -134,6 +134,17 @@ config BOOT_TRACER
>  	  be enabled if this tracer is selected since only one tracer
>  	  should touch the tracing buffer at a time.
>  
> +config POWER_TRACER
> +	bool "Trace power consumption behavior"
> +	depends on DEBUG_KERNEL
> +	depends on X86
> +	select TRACING

this should be HAVE_POWER_TRACER defined in arch/x86/Kconfig, instead 
of a 'depends on X86'.

> +	help
> +	  This tracer helps developers to analyize and optimize the kernels
> +	  power management decisions, specifically the C-state and P-state
> +	  behavior.

s/analyize/analyse
s/kernels/kernel's

> +static struct trace_array *power_trace;
> +static int trace_power_enabled;

__read_mostly ?

	Ingo