linux-kernel - Re: [PATCH][RFC] tracing: Enable tracepoints via module parameters

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Message-ID: <1154727029.2004.1618925367044.JavaMail.zimbra@efficios.com>
Date:   Tue, 20 Apr 2021 09:29:27 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     rostedt <rostedt@...dmis.org>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        fweisbec <fweisbec@...il.com>, Jessica Yu <jeyu@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...e.hu>, chris@...is-wilson.co.uk,
        yuanhan liu <yuanhan.liu@...ux.intel.com>,
        "Grumbach, Emmanuel" <emmanuel.grumbach@...el.com>
Subject: Re: [PATCH][RFC] tracing: Enable tracepoints via module parameters

----- On Apr 20, 2021, at 8:55 AM, rostedt rostedt@...dmis.org wrote:
[...]
> 
> Would adding automatic module parameters be an issue? That is, you can add
> in the insmod command line a parameter that will enable tracepoints. We
> could have a way to even see them from the modinfo. I think I had that
> working once, and it wasn't really that hard to do.

There is one thing we should consider here in terms of namespacing: those module
command line parameters should be specific to each tracer (e.g. ftrace, perf, ebpf).

LTTng for instance already tackles early module load tracing in a different
way: users can enable instrumentation of yet-to-be loaded kernel modules. So
it would not make sense in that scheme to have module load parameters.

It's a different trade-off in terms of error reporting though: for instance,
LTTng won't report an error if a user does a typo when entering an event name.

So I think those command line parameters should be tracer-specific, do you agree ?

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com