linux-kernel - Re: [PATCH v9 04/10] x86: refcount: prevent gcc distortions

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Date:   Thu, 04 Oct 2018 01:40:20 -0700
From:   hpa@...or.com
To:     Ingo Molnar <mingo@...nel.org>, Nadav Amit <namit@...are.com>
CC:     Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        x86@...nel.org, Thomas Gleixner <tglx@...utronix.de>,
        Jan Beulich <JBeulich@...e.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH v9 04/10] x86: refcount: prevent gcc distortions

On October 4, 2018 1:33:33 AM PDT, Ingo Molnar <mingo@...nel.org> wrote:
>
>* Ingo Molnar <mingo@...nel.org> wrote:
>
>> I'm also somewhat annoyed at the fact that this series carries a
>boatload
>> of reviewed-by's and acked-by's, yet none of those reviewers found it
>> important to point out the large chasm that is gaping between
>description
>> and reality.
>
>Another problem I just realized is that we now include
>arch/x86/kernel/macros.S in every 
>translation pass when building the kernel, right?
>
>But arch/x86/kernel/macros.S expands to a pretty large hiearchy of
>header files:
>
>  $ make arch/x86/kernel/macros.s
>
>$ cat $(grep include arch/x86/kernel/macros.s | cut -d\" -f2 | sort |
>uniq) | wc -l
>  4128
>
>That's 4,100 extra lines of code to be preprocessed for every
>translation unit, of
>which there are tens of thousands. More if other pieces of code get
>macrofied in
>this fasion in the future.
>
>If we assume that a typical distribution kernel build has ~20,000
>translation units
>then this change adds 82,560,000 more lines to be preprocessed, just to
>work around
>a stupid GCC bug?
>
>I'm totally unhappy about that. Can we do this without adding macros.S?
>
>It's also a pretty stupidly central file anyway that moves source code
>away
>from where it's used.
>
>Thanks,
>
>	Ingo

It's not just for working around a stupid GCC bug, but it also has a huge potential for cleaning up the inline asm in general.

I would like to know if there is an actual number for the build overhead (an actual benchmark); I have asked for that once already.
-- 
Sent from my Android device with K-9 Mail. Please excuse my brevity.