linux-kernel - Re: [PATCHv2] locking/atomics: build atomic headers as required

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Message-ID: <20181210175355.brnmlzj5g5mbhuz2@lakrids.cambridge.arm.com>
Date:   Mon, 10 Dec 2018 17:53:55 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Borislav Petkov <bp@...e.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will.deacon@....com>
Subject: Re: [PATCHv2] locking/atomics: build atomic headers as required

Hi Ingo,

On Thu, Dec 06, 2018 at 05:13:44PM +0100, Ingo Molnar wrote:
> 
> * Mark Rutland <mark.rutland@....com> wrote:
> 
> > Andrew and Ingo report that the check-atomics.sh script is simply too
> > slow to run for every kernel build, and it's impractical to make it
> > faster without rewriting it in something other than shell.
> > 
> > Rather than committing the generated headers, let's regenerate these
> > as-required, if we change the data or scripts used to generate the
> > atomic headers, or when building from a pristine tree.
> > 
> > That ensures they're always up-to-date, allows them to be built in
> > parallel, and avoid redundant rebuilds, which is a 2-8s saving per
> > incremental build. Since the results are not committed, it's very
> > obvious that they should not be modified directly. If we need to
> > generate more headers in future, it's easy to extend Makefile.genheader
> > to permit this.

> So these 'automatically generated' headers are actual and important code, 
> and I think it's bad practice to remove these from the git grep search 
> space and history as well.
> 
> Really, this whole notion of auto-generating the headers should be 
> implemented correctly, instead of working around deficiencies in a 
> short-term fashion that introduces other deficiencies.
> 
> I never got any replies to my previous comments about this:
> 
>   <20181128083057.GA7879@...il.com>

As I've just mentioned in another thread, I've sent out a couple of patches
attempting to address this while leaving the headers checked-in:

https://lkml.kernel.org/r/20181210175035.45096-1-mark.rutland@arm.com

Thanks,
Mark.