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

hpa
2018-10-04T08:40:38Z

On October 4, 2018 1:33:33 AM PDT, Ingo Molnar <mingo@kernel.org> wrote:
>
>* Ingo Molnar <mingo@kernel.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.
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