linux-kernel - Re: [bloat] Measuring header file bloat effects on kernel build performance: a more than 2x slowdown ...

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Message-ID: <20110523161914.GA15464@merkur.ravnborg.org>
Date:	Mon, 23 May 2011 18:19:14 +0200
From:	Sam Ravnborg <sam@...nborg.org>
To:	Ingo Molnar <mingo@...e.hu>, Christopher Li <sparse@...isli.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	David Miller <davem@...emloft.net>, linux-next@...r.kernel.org,
	linux-kernel@...r.kernel.org, x86@...nel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [bloat] Measuring header file bloat effects on kernel build
	performance: a more than 2x slowdown ...

> 
> Such thing happen due to:
> 
>  - header files only get added, almost never removed
> 
> The key thing was that the build did not break when prefetch.h was kept 
> dangling. Not sure what to do about that - for humans a dangling header is 
> absolutely non-obvious to find - we'd need tooling help.

Long time ago I discussed this briefly with Christopher Li,
and he hacked support for this in sparse.

The branch is still around:

http://git.kernel.org/?p=devel/sparse/chrisl/sparse.git;a=shortlog;h=unused-include-files

I never got around to play with it for various reasons.
IIRC it will list include files not used in _current_ configuration,
so use if CONFIG_ etc. may give different results.

	Sam
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