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Date: Mon, 23 May 2011 13:21:22 +0300
Message-ID: <BANLkTi=Vbr+DRBy6sa7omGpvAb0uGunYMA@mail.gmail.com>
Subject: Re: [bloat] Measuring header file bloat effects on kernel build
 performance: a more than 2x slowdown ...
From: Alexey Dobriyan <adobriyan@gmail.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Stephen Rothwell <sfr@canb.auug.org.au>,
        Thomas Gleixner <tglx@linutronix.de>, "H. Peter Anvin" <hpa@zytor.com>,
        David Miller <davem@davemloft.net>, linux-next@vger.kernel.org,
        linux-kernel@vger.kernel.org, x86@kernel.org,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Andrew Morton <akpm@linux-foundation.org>
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On Mon, May 23, 2011 at 12:09 PM, Ingo Molnar <mingo@elte.hu> wrote:
>      24594a2bfcaa: [PATCH] x86-64 merge
>
>     - Remove some unneeded prefetches.  Just two are enough to kickstart
>       the hardware prefetcher.
>
>   But despite touching prefetches explicitly, this too sloppily left the (now
>   dangling) prefetch.h include file around.

Well, developer removes include, developer risks compile breakage.

> Anway, what i tried to demonstrate with this mail how much *real* slowdown in
> the kernel build our current header file bloat is causing. We could literally
> halve our kernel build times if we fixed this!

News at 11!

Ingo, you're running x86 compile tests nonstop, you can very well make asm-x86
headers the strictest ones to make problem less problematic.

You (x86 merge people), removed header guards from quite a lot of asm-x86/*.h
files breaking gcc "do not open(2) second time" heuristics. It became better
since last I've noticed it, but maybe start with that?