Re: [PATCH 1/2 v2] tracing/function-graph-tracer: various fixes and features

[Ingo Molnar <mingo@elte.hu>]

* Frederic Weisbecker <fweisbec@gmail.com> wrote:

> 
> This patch brings various bugfixes:
> 
> _ Drop the first irrelevant task switch on the very beginning of a trace.
> _ Drop the OVERHEAD word from the headers, the DURATION word is sufficient and will not
>   overlap other columns.
> _ Make the headers fit well their respective columns whatever the selected options.

> About features, one can now disable the duration (this will hide the 
> overhead too for convenient reasons and because on doesn't need overhead 
> if it hasn't the duration

very nice! I've applied this to tip/tracing/function-graph-tracer, thanks 
Frederic!

this:

> I guess no one needs the nanosec precision here, the main goal is to 
> find when happened the events on a cpu when the trace switches from one 
> cpu to another.
> 
> ie:
> 
>   274.874760 |   1)   0.676 us    |      _spin_unlock();
>   274.874762 |   1)   0.609 us    |      native_load_sp0();
>   274.874763 |   1)   0.602 us    |      native_load_tls();
>   274.878739 |   0)   0.722 us    |                  }
>   274.878740 |   0)   0.714 us    |                  native_pmd_val();
>   274.878741 |   0)   0.730 us    |                  native_pmd_val();
> 
> Here there is a 4000 usecs difference when we switch the cpu.

Still needs a solution - if we do cross-CPU traces we want to have a 
global trace clock with 'seemless' transition between CPUs.

	Ingo