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

* 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


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