linux-kernel - Re: [PATCH] ftrace: add simple oneshot function tracer

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Message-ID: <20190626120412.662e8cf9@gandalf.local.home>
Date:   Wed, 26 Jun 2019 12:04:12 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Thomas Preisner <linux@...eisner.de>
Cc:     Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ftrace: add simple oneshot function tracer

On Sun, 23 Jun 2019 14:05:55 +0200
Thomas Preisner <linux@...eisner.de> wrote:


> I've created this tracer with kernel tailoring in mind since the
> tailoring process of e.g. undertaker heavily benefits from a more
> precise set of input data.
> 
> A "oneshot" option for the function tracer would be a viable
> possibility. However, this may add a lot of overhead (performance wise)
> in comparison to my current approach? After all, the use case of my
> tracer would be some sort of kernel activity monitoring during "normal
> usage" in order to get a grasp of (hopefully) all required kernel
> functions.

Coming back from vacation and not having this threaded in my inbox,
I have to ask (to help cache this back into my head), what was the
"current approach" compared to the "oneshot" option, and why would it
have better performance?

> 
> Also, there is no strong reason to add a new event type,
> this was just a means of reducing the collected data (which may as well
> be omitted since there is no real benefit).

+1

> 
> My "oneshot tracer" actually collects and outputs every parent in order
> to get a more thorough view on used kernel code. Therefore, I would
> suggest to keep this functionality and maybe make it configurable
> instead?

Configure which? (again, coming back from vacation, I need a refresher
on this ;-)

-- Steve