linux-kernel - Re: [PATCH 3/3] utrace-based ftrace "process" engine, v2

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Date:	Mon, 23 Mar 2009 13:39:22 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	"Frank Ch. Eigler" <fche@...hat.com>
cc:	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Roland McGrath <roland@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>, utrace-devel@...hat.com,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 3/3] utrace-based ftrace "process" engine, v2



On Mon, 23 Mar 2009, Frank Ch. Eigler wrote:
> > I have CONFIG_DEBUG_INFO turned off in 99.9% of my kernel builds, 
> > because it slows down the kernel build times significantly: [...]
> 
> OK, 15% longer time.

It's way more than that if you don't have tons of memory and excessive 
amounts of CPU power.

> > 2)
> > 
> > When the kernel build becomes IO-bound [...]
> >   without:   870.36 user 292.79 system 3:32.10 elapsed  548% CPU
> >   with:      929.65 user 384.55 system 8:28.70 elapsed  258% CPU
> 
> OK, lots of network traffic.

This is the _normal_ situation for a debug info build.  If it's not 
network traffic (distcc), it's just disk IO. Have you tried it on a 
laptop? Ingo is not the only one that turns off DEBUG_INFO in disgust. 
It's totally useless for any sane kernel developer - the costs are 
excessive.

Adn that's totally ignoring the disk usage of multiple debug info kernels.

> Note that this backs away from earlier claims that we can make do
> without debuginfo, or that the compiler can't be trusted to build the
> stuff.  We all agree it'd be nice if made it better and made a little
> less.

Gaah. I'd wish you all agreed that DEBUG_INFO is just TOTALLY UNREALISTIC.

			Linus
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