linux-kernel - Re: [PATCH 1/2] Makefile: Fix distcc compilation with x86 macros

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Message-ID: <40E4E1B4-EF5F-43A1-B42C-C4CF6349FC62@vmware.com>
Date:   Tue, 13 Nov 2018 17:55:36 +0000
From:   Nadav Amit <namit@...are.com>
To:     Ingo Molnar <mingo@...nel.org>
CC:     Ingo Molnar <mingo@...hat.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Logan Gunthorpe <logang@...tatee.com>
Subject: Re: [PATCH 1/2] Makefile: Fix distcc compilation with x86 macros

From: Ingo Molnar
Sent: November 13, 2018 at 11:30:00 AM GMT
> To: Nadav Amit <namit@...are.com>
> Cc: Ingo Molnar <mingo@...hat.com>, Masahiro Yamada <yamada.masahiro@...ionext.com>, Michal Marek <michal.lkml@...kovi.net>, Thomas Gleixner <tglx@...utronix.de>, Borislav Petkov <bp@...en8.de>, H. Peter Anvin <hpa@...or.com>, x86@...nel.org, linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org
> Subject: Re: [PATCH 1/2] Makefile: Fix distcc compilation with x86 macros
> 
> 
> 
> * Nadav Amit <namit@...are.com> wrote:
> 
>> Introducing the use of asm macros in c-code broke distcc, since it only
>> sends the preprocessed source file. The solution is to break the
>> compilation into two separate phases of compilation and assembly, and
>> between the two concatanate the assembly macros and the compiled (yet
> 
> s/concatenate
> 
>> not assembled) source file. Since this is less efficient, this
>> compilation mode is only used when make is called with the "DISTCC=y"
>> parameter.
>> 
>> Note that the assembly stage should also be distributed, if distcc is
>> configured using "CFLAGS=-DENABLE_REMOTE_ASSEMBLE".
> 
> It's a bit sad that we regressed distcc performance …

I don’t know what the actual impact is, but Logan, who reported the bug says
there is an alternative solution for when distcc-pump is used (which
presumably would have ~zero performance degradation). distcc is really
fragile IMHO - it’s enough that it finds what looks like two source files in
the compiler command arguments for it to fall back to local compilation.

[ In this regard, the distcc-pump solution would *not* work if distcc is
built with support for distributed assembly, since it will consider the .s
file as a second source file. ]

>> +# If distcc is used, then when an assembly macro files is needed, the
>> +# compilation stage and the assembly stage need to be separated. Providing
>> +# "DISTCC=y" option enables the separate compilation and assembly.
> 
> Let's fix the various typos:
> 
>> +# If distcc is used, and when assembly macro files are needed, the
>> +# compilation stage and the assembly stage needs to be separated. 
>> +# Providing the "DISTCC=y" option enables separate compilation and 
>> +# assembly.

That’s grammar, not typos ;-)

Sorry for that - I will fix it an send v2 (as well as the whitespace noise).

Regards,
Nadav