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

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Message-Id: <20181123150943.ddf22393b568131a3383fd02@linux-foundation.org>
Date:   Fri, 23 Nov 2018 15:09:43 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Mark Rutland <mark.rutland@....com>
Cc:     linux-kernel@...r.kernel.org, mingo@...nel.org,
        Boqun Feng <boqun.feng@...il.com>,
        Borislav Petkov <bp@...e.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will.deacon@....com>
Subject: Re: [PATCH] locking/atomics: build atomic headers as required

On Fri, 23 Nov 2018 15:33:21 +0000 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 for 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.
> 
> I've verified that this works in the cases we previously had issues with
> (out-of-tree builds and where scripts have no execute permissions), and
> have tested these cases for both x86_64 and arm64.

Seems like a reasonable compromise.  I'll take a copy for testing now,
shall drop that when this appears in tip->linux-next.