linux-kernel - Re: ftrace behaviour (was: [PATCH] ftrace: introduce tracing_reset_online

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Message-ID: <20090101000812.1fd2c088@iki.fi>
Date:	Thu, 1 Jan 2009 00:08:12 +0200
From:	Pekka Paalanen <pq@....fi>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Frédéric Weisbecker <fweisbec@...il.com>,
	Pekka J Enberg <penberg@...helsinki.fi>, mingo@...e.hu,
	linux-kernel@...r.kernel.org,
	Markus Metzger <markus.t.metzger@...il.com>
Subject: Re: ftrace behaviour (was: [PATCH] ftrace: introduce
 tracing_reset_online_cpus() helper)

On Wed, 31 Dec 2008 14:06:26 -0500 (EST)
Steven Rostedt <rostedt@...dmis.org> wrote:

> I was thinking of only changing the debugfs file.
> 
> > Are we controlling an action (recording events), a feature (a buffer
> > where to record) or an implementation (a ring buffer)?
> 
> Good point. It only disables the recording, so perhaps a "record_enabled" 
> would be better?

To me "record" sounds more of a noun than a verb, but it's both and
I'm not a native speaker. Still, it brings me to "recording_enabled",
and do we really need the "_enabled" part? So we end up to what I
suggested earlier: "recording" with values 0 and 1. :-)

Anyway, it's good to start the file name with a few distinct letters,
it makes tab-completion so much easier on the command line.

> > What does the user actually want to control? A buffer? A ring
> > buffer? Recording stuff? The tracer? Tracing? Data flow?
> > Assuming there are also other users than tracing, does it make
> > sense to control the ring buffer facility itself?
> 
> I think the name record_enabled for debugfs is the best. This is exactly 
> what happens (not how it is implemented). When someone echos 0 to 
> record_enabled (currently called tracing_on), it stops the recording, and 
> nothing else. The tracers still try to write to the buffer, but the write 
> always fails. This does not disable the tracers or even notify the tracer 
> that the buffers have stopped recording. This is just a simple light 
> weight way to stop and start recording to the trace buffers from either 
> user space or kernel space.  Kernel space can stop it, and user space can 
> start it again (that was the original request for this feature).
> 
> I'm leaning towards record_enabled now.

-- 
Pekka Paalanen
http://www.iki.fi/pq/
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