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SubjectRe: Enable histograms for events/ftrace/timerlat and osnoise
On Mon, 27 Mar 2023 14:37:11 +0200
Daniel Bristot de Oliveira <bristot@redhat.com> wrote:

> 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)?

No, I think we just missed not creating the "hist" file, which should not
actually exist.

>
> am I missing something?
>
> > How hard would it be to enable histograms to the ftrace/osnoise and
> > ftrace/timerlat events?

I'll try to get some time to look at this. No guarantees :-p

-- Steve

> >
> > This will allow me to reduce the overhead of rtla timerlat and rtla osnoise
> > tools...
> >
> > Thanks in advance, Stephen!
> > -- Denny

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