linux-kernel - [performance problem] CONFIG_DYNAMIC_FTRACE: Increased kernel build times

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Date:	Fri, 23 Oct 2009 09:45:33 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Steven Rostedt <rostedt@...dmis.org>,
	Frédéric Weisbecker <fweisbec@...il.com>
Cc:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: [performance problem] CONFIG_DYNAMIC_FTRACE: Increased kernel
	build times

Steve,

i did an 64-bit allyesconfig build test (with debug_info disabled), with 
and without CONFIG_DYNAMIC_FTRACE set.

The build time results are:

  -CONFIG_DYNAMIC_FTRACE:   266.30
  +CONFIG_DYNAMIC_FTRACE:   296.07 (+11.2%)

So we get more than 10% build time overhead.

That's quite high - higher than what i remember having measured 
originally when the first iteration of the mcount code went in.

This extra overhead comes from the mcount post-processing script 
(scripts/recordmcount.pl) that runs objcopy as well and is written in 
Perl. I think this whole angle needs to be improved - 10% is way too 
high of a price to pay.

	Ingo
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