linux-kernel - Re: [PATCH] ftrace: introduce tracing_reset_online

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Date:	Sat, 20 Dec 2008 14:15:08 +0100
From:	"Frédéric Weisbecker" <fweisbec@...il.com>
To:	"Steven Rostedt" <rostedt@...dmis.org>
Cc:	"Pekka J Enberg" <penberg@...helsinki.fi>, mingo@...e.hu,
	linux-kernel@...r.kernel.org, "Pekka Paalanen" <pq@....fi>,
	"Markus Metzger" <markus.t.metzger@...il.com>
Subject: Re: [PATCH] ftrace: introduce tracing_reset_online_cpus() helper

2008/12/19 Steven Rostedt <rostedt@...dmis.org>:
>
> On Fri, 19 Dec 2008, Fr?d?ric Weisbecker wrote:
>>
>>
>> That's looks good.
>> By the past, I also suggested Steven to automatically reset the traces
>> buffer each time a tracer is started, that
>> would factor out the code a bit more. I don't think one tracer would
>> avoid to reset the buffer once it is started, and
>> I don't think it is needed to reset twice on tracer switching: on stop
>> of the old tracer and on start on the new. Only
>> on start should be enough.
>
> I'm actually against the idea of reseting a trace everytime we enable it.
> That is:
>
> echo 1 > /debug/tracing/tracing_enabled
>
> This should not reset the tracer. I actually do tracing where I disable
> and enable it around areas I am interested in. I want all tracing, not
> just the last one.
>
> Now we have recently added /debug/tracing/tracing_on which can quickly
> stop tracing. I may be able to use that, and we can let the
> tracing_enable" reset it too.
>
> I'll have to take a look at my scripts to see if that would work.


Ok.
Actually perhaps that could be useful to do it only before calling the
init callback of a tracer.
That should be the only place where a tracer would want to reset the buffers....
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