linux-kernel - Re: [RFA][PATCH] tracing: Add trace_<tracepoint>

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Message-ID: <20140506170640.088df53b@gandalf.local.home>
Date:	Tue, 6 May 2014 17:06:40 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Javi Merino <javi.merino@....com>,
	David Howells <dhowells@...hat.com>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [RFA][PATCH] tracing: Add trace_<tracepoint>_enabled() function

On Tue, 6 May 2014 20:53:41 +0000 (UTC)
Mathieu Desnoyers <mathieu.desnoyers@...icios.com> wrote:


> > I do plan on adding more documentation to this to stress that this
> > should be done like this. But hey, we're kernel developers, we should
> > be responsible enough to not require the hand holding.
> 
> I like your optimism. ;-)

I'm always the optimist :-)

> > The first time I thought about using this was with David's code, which
> > does this:
> > 
> > 	if (static_key_false(&i2c_trace_msg)) {
> > 		int i;
> > 		for (i = 0; i < ret; i++)
> > 			if (msgs[i].flags & I2C_M_RD)
> > 				trace_i2c_reply(adap, &msgs[i], i);
> > 		trace_i2c_result(adap, i, ret);
> > 	}
> > 
> > That would look rather silly in a tracepoint.
> 
> Which goes with a mandatory silly question: how do you intend mapping
> the single key to two different tracepoints ?

Could always do:

	if (trace_i2c_result_enabled() || trace_i2c_reply_enabled()) {

I wounder what the assembly of that would look like.

Still, having "side-effects" in the tracepoint parameters just seems
odd to me.

- Steve
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