Re: [PATCH v4 08/10] libtracefs: Use the internal dynamic events API when creating synthetic events

[Steven Rostedt <rostedt@goodmis.org>]

On Fri, 5 Nov 2021 14:15:05 +0200
Tzvetomir Stoyanov <tz.stoyanov@gmail.com> wrote:

> I looked and tested more this code today, but as I understood the
> instance is mandatory in histograms creation and should not be removed
> from this API. That API appends the histogram config in the event's
> trigger files, which is for specific instances. The histogram is
> accumulated only in the context of that instance. I'm going to send
> next version of the patch set, but without changes to this API.

The histogram code is internal to the synthetic events. That's because it
uses the histogram to save the data across the start to end event to create
the synthetic event. The histogram is an implementation detail of the
synthetic event and should not be exposed via the API. And that is
*exactly* why instances should not be exposed to the synthetic event!

In fact, I don't wan the user to have control over the instances because
they are likely to screw it up if they don't know what they are doing.
That's why I suggested to convert the current API into a raw event, because
to use instances, you had better know what you are doing, otherwise you can
easily screw it up.

The histograms used by synthetic events are "special" and if not done
properly, will not do what people expect.

If you don't want to make this change, I will.

-- Steve