Re: [PATCH 2/2] tools, perf: Documentation for the power events API
From: Eduardo Valentin
Date: Fri Jan 07 2011 - 00:56:35 EST
On Wed, Jan 05, 2011 at 07:49:02PM +0100, ext jean.pihet@xxxxxxxxxxxxxx wrote:
> From: Jean Pihet <j-pihet@xxxxxx>
> Provides documentation for the following:
> - the new power trace API,
> - the old (legacy) power trace API,
> - the DEPRECATED Kconfig option usage.
> Signed-off-by: Jean Pihet <j-pihet@xxxxxx>
> Documentation/trace/events-power.txt | 90 ++++++++++++++++++++++++++++++++++
> 1 files changed, 90 insertions(+), 0 deletions(-)
> create mode 100644 Documentation/trace/events-power.txt
> diff --git a/Documentation/trace/events-power.txt b/Documentation/trace/events-power.txt
> new file mode 100644
> index 0000000..96d87b6
> --- /dev/null
> +++ b/Documentation/trace/events-power.txt
> @@ -0,0 +1,90 @@
> + Subsystem Trace Points: power
> +The power tracing system captures events related to power transitions
> +within the kernel. Broadly speaking there are three major subheadings:
> + o Power state switch which reports events related to suspend (S-states),
> + cpuidle (C-states) and cpufreq (P-states)
> + o System clock related changes
What do you mean by system clock here? I see that you are covering cpu rate
changes and system clock (?) here. How about memory clock changes?
Would it make sense to have a major subheading for it? Maybe you are
targeting it be traced by means of clocks event (item 2. bellow)..
> + o Power domains related changes and transitions
> +This document describes what each of the tracepoints is and why they
> +might be useful.
> +Cf. include/trace/events/power.h for the events definitions.
> +1. Power state switch events
> +1.1 New trace API
> +A 'cpu' event class gathers the CPU-related events: cpuidle and
> +cpu_idle "state=%lu cpu_id=%lu"
> +cpu_frequency "state=%lu cpu_id=%lu"
> +A suspend event is used to indicate the system going in and out of the
> +suspend mode:
> +machine_suspend "state=%lu"
> +Note: the value of '-1' or '4294967295' for state means an exit from the current state,
> +i.e. trace_cpu_idle(4, smp_processor_id()) means that the system
> +enters the idle state 4, while trace_cpu_idle(PWR_EVENT_EXIT, smp_processor_id())
> +means that the system exits the previous idle state.
> +The event which has 'state=4294967295' in the trace is very important to the user
> +space tools which are using it to detect the end of the current state, and so to
> +correctly draw the states diagrams and to calculate accurate statistics etc.
> +1.2 DEPRECATED trace API
> +A new Kconfig option CONFIG_EVENT_POWER_TRACING_DEPRECATED with the default value of
> +'y' has been created. This allows the legacy trace power API to be used conjointly
> +with the new trace API.
> +The Kconfig option, the old trace API (in include/trace/events/power.h) and the
> +old trace points will disappear in a future release (namely 2.6.41).
> +power_start "type=%lu state=%lu cpu_id=%lu"
> +power_frequency "type=%lu state=%lu cpu_id=%lu"
> +power_end "cpu_id=%lu"
> +The 'type' parameter takes one of those macros:
> + . POWER_NONE = 0,
> + . POWER_CSTATE = 1, /* C-State */
> + . POWER_PSTATE = 2, /* Fequency change or DVFS */
> +The 'state' parameter is set depending on the type:
> + . Target C-state for type=POWER_CSTATE,
> + . Target frequency for type=POWER_PSTATE,
> +power_end is used to indicate the exit of a state, corresponding to the latest
> +power_start event.
> +2. Clocks events
> +The clock events are used for clock enable/disable and for
> +clock rate change.
> +clock_enable "%s state=%lu cpu_id=%lu"
> +clock_disable "%s state=%lu cpu_id=%lu"
> +clock_set_rate "%s state=%lu cpu_id=%lu"
> +The first parameter gives the clock name (e.g. "gpio1_iclk").
> +The second parameter is '1' for enable, '0' for disable, the target
> +clock rate for set_rate.
> +3. Power domains events
> +The power domain events are used for power domains transitions
> +power_domain_target "%s state=%lu cpu_id=%lu"
> +The first parameter gives the power domain name (e.g. "mpu_pwrdm").
> +The second parameter is the power domain target state.
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