linux-kernel - Re: [PATCH 1/2] ftrace: Add separate handler for ftrace:function event

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Message-ID: <20151125120257.17e53cab@gandalf.local.home>
Date:	Wed, 25 Nov 2015 12:02:57 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	Jiri Olsa <jolsa@...nel.org>, lkml <linux-kernel@...r.kernel.org>,
	David Ahern <dsahern@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...nel.org>
Subject: Re: [PATCH 1/2] ftrace: Add separate handler for ftrace:function
 event

On Wed, 25 Nov 2015 17:50:57 +0100
Jiri Olsa <jolsa@...hat.com> wrote:

> > This seems redundant. I never understood the control_ops that perf uses
> > in the function tracing infrastructure. Why can't you just register the
> > event->ops and have that ops set the filtering? Then the ftrace
> > infrastructure will only call that event handler for the functions its
> > filtered on. Then you don't need to do it again. Right now ftrace
> > already does that with the generic "control_ops" that perf uses, but
> > now you are doing it again. Seems rather pointless.  
> 
> well thats exactly what we are doing.. but as all ops
> share single callback we need to find the proper event
> this callback was triggered for

The ftrace_ops has a "private" field for the user to set. Could you
make that point back to the event that allocated the ftrace_ops?
Then the callback function could easily get the event that matches the
ftrace_ops.

> 
> currently we use tracepoint callback (perf_tp_event)
> where the proper event is found based on the event->filter
> 
> however this is not the case for ftrace:function because
> filter will not change the event->filter, but the ops filter

Yeah, I'm trying to figure out the paths here. I would love to remove
the control_ops as that complicates the function tracing code a bit
more than I would like it to be.

I just crashed function tracing by function tracing perf doing function
tracing :-) I'm currently debugging that (and adding more code to help
debug things like this).

-- Steve


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