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

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Date:	Fri, 23 Oct 2009 12:18:41 +0200 (CEST)
From:	John Kacur <jkacur@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [performance problem] CONFIG_DYNAMIC_FTRACE: Increased kernel 
 build times

2009/10/23 Ingo Molnar <mingo@...e.hu> wrote:
> 
> 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.

Hi Ingo, do you still have the profiling data to share with us?
Was the problem more in objcopy / objdump, rather than in the perl script 
itself?

Thanks

John