linux-kernel - Re: [PATCH] tracing: remove superfluous sub instructions

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Date:	Tue, 18 Jan 2011 12:01:17 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	Frederic Weisbecker <fweisbec@...il.com>, mingo@...e.hu,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tracing: remove superfluous sub instructions

On Tue, 2011-01-18 at 17:41 +0100, Jiri Olsa wrote:

> ops, missed this one..
> 
> would it make sense to update the IP inside the function_trace_probe_call
> function to save one instruction in the entry code used by all? or it's
> not worth it..

That would require function_trace_probe_call() to handle arch
dependencies. I would like to keep arch dependent code in the arch
subsystem when possible.

This change only saves a subtraction to a register. It only gets called
if we are tracing functions. This modification is far into the noise
that is caused by the tracer. I don't think it is worth it as it will
cause head aches with knowing how to handle the ip from the users of the
function tracer.

I do plan on making the function tracer a bit more generic for common
users. I would like to keep the ip at the call site of mcount.

-- Steve

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