Re: [PATCH V2] tracing, perf : add cpu hotplug trace events

[Frederic Weisbecker <fweisbec@gmail.com>]

On Fri, Jan 21, 2011 at 09:43:18AM +0100, Vincent Guittot wrote:
> On 20 January 2011 17:11, Frederic Weisbecker <fweisbec@gmail.com> wrote:
> > On Thu, Jan 20, 2011 at 09:25:54AM +0100, Vincent Guittot wrote:
> >> Please find below a new proposal for adding trace events for cpu hotplug.
> >> The goal is to measure the latency of each part (kernel, architecture)
> >> and also to trace the cpu hotplug activity with other power events. I
> >> have tested these traces events on an arm platform.
> >>
> >> Changes since previous version:
> >> -Use cpu_hotplug for trace name
> >> -Define traces for kernel core and arch parts only
> >> -Use DECLARE_EVENT_CLASS and DEFINE_EVENT
> >> -Use proper indentation
> >>
> >> Subject: [PATCH] cpu hotplug tracepoint
> >>
> >> this patch adds new events for cpu hotplug tracing
> >>  * plug/unplug sequence
> >>  * core and architecture latency measurements
> >>
> >> Signed-off-by: Vincent Guittot <vincent.guittot@linaro.com>
> >> ---
> >>  include/trace/events/cpu_hotplug.h |  117 ++++++++++++++++++++++++++++++++++++
> >
> > Note we can't apply new tracepoints if they are not inserted in the code.
> 
> I agree, i just want to have 1st feedbacks on the tracepoint interface
> before providing a patch which inserts the trace in the code.
> 
> >
> >> +DEFINE_EVENT(cpu_hotplug, cpu_hotplug_arch_wait_die_start,
> >> +
> >> +     TP_PROTO(unsigned int cpuid),
> >> +
> >> +     TP_ARGS(cpuid)
> >> +);
> >> +
> >> +DEFINE_EVENT(cpu_hotplug, cpu_hotplug_arch_wait_die_end,
> >> +
> >> +     TP_PROTO(unsigned int cpuid),
> >> +
> >> +     TP_ARGS(cpuid)
> >> +);
> >
> > What is wait die, compared to die for example?
> >
> 
> The arch_wait_die is used to trace the process which waits for the cpu
> to die (__cpu_die) and the arch_die is used to trace when the cpu dies
> (cpu_die)

I still can't find the difference.

Having:

trace_cpu_hotplug_arch_die_start(cpu)
__cpu_die();
trace_cpu_hotplug_arch_die_end(cpu)

Is not enough to get both the information that a cpu dies
and the time took to do so?