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Date: Thu, 13 Jun 2024 11:36:10 +0100
From: Mark Rutland <mark.rutland@arm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Boqun Feng <boqun.feng@gmail.com>, rust-for-linux@vger.kernel.org,
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Subject: Re: [RFC 1/2] rust: Introduce atomic API helpers
Message-ID: <ZmrLmnPz_0Q8oXny@J2N7QTR9R3>
References: <20240612223025.1158537-1-boqun.feng@gmail.com>
 <20240612223025.1158537-2-boqun.feng@gmail.com>
 <2024061341-whole-snowfall-89a6@gregkh>
 <20240613091747.GB17707@noisy.programming.kicks-ass.net>
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On Thu, Jun 13, 2024 at 11:17:47AM +0200, Peter Zijlstra wrote:
> On Thu, Jun 13, 2024 at 07:38:51AM +0200, Greg Kroah-Hartman wrote:
> > On Wed, Jun 12, 2024 at 03:30:24PM -0700, Boqun Feng wrote:
> > > +// Generated by scripts/atomic/gen-rust-atomic-helpers.sh
> > > +// DO NOT MODIFY THIS FILE DIRECTLY
> > 
> > Why not just build this at build time and not check the file into the
> > tree if it is always automatically generated?  That way it never gets
> > out of sync.  We do this for other types of auto-generated files in the
> > kernel today already.
> 
> Part of the problem is, is that a *TON* of files depend on the atomic.h
> headers. If we'd generate it on every build, you'd basically get to
> rebuild the whole kernel every single time.
> 
> Also, these files don't change too often. And if you look, there's a
> hash in those files which is used to check if things somehow got stale.

That and:

1) The generation is currently slow (multiple seconds), which gets
   people angry if they have to wait for it for a clean build. Improving
   that would require changing the way we generate the headers (e.g.
   rewrite that in something else to avoid the subshell fork problem).

   Last I looked there wasn't an obvious better way to do this, because
   nice options ended up pulling in more build-time dependencies.

2) Linus wanted git grep to work, which meant checking in the generated
   files:

   https://lore.kernel.org/all/CA+55aFxjU0op8QLLu0n-RjHBs7gQsLvD8jcyedgw6jeZFN7B+Q@mail.gmail.com/

Mark.