Re: Enable histograms for events/ftrace/timerlat and osnoise

[Daniel Bristot de Oliveira]

On 3/24/23 17:13, Daniel Bristot de Oliveira wrote:
> Hi Steven
> 
> I would like to collect histograms from timerlat and osnoise tracers event,
> but I cannot collect them because they are not tracepoints but... tracer
> events. So...
> 
>   # ls /sys/kernel/tracing/events/ftrace/timerlat/
>   format	hist
> 
> no hist, filter, trigger files...

Ooop, the hist file exists, what is missing is the trigger file, which is
used to enable the histogram...

it seems that the "limitation" is around TRACE_EVENT_FL_IGNORE_ENABLE flag, and
the fact that ftrace events cannot be enabled/disabled... 

but wait, as the hist file exist, is there any other way to enable
the histogram? (or should we disable hist files for !TRACE_EVENT_FL_IGNORE_ENABLE)?

am I missing something?

> How hard would it be to enable histograms to the ftrace/osnoise and
> ftrace/timerlat events?
> 
> This will allow me to reduce the overhead of rtla timerlat and rtla osnoise
> tools...
> 
> Thanks in advance, Stephen!
> -- Denny