linux-kernel - Re: [RFC 1/2] rust: Introduce atomic API helpers

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Message-ID: <ZmrLmnPz_0Q8oXny@J2N7QTR9R3>
Date: Thu, 13 Jun 2024 11:36:10 +0100
From: Mark Rutland <mark.rutland@....com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Boqun Feng <boqun.feng@...il.com>, rust-for-linux@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	llvm@...ts.linux.dev, Miguel Ojeda <ojeda@...nel.org>,
	Alex Gaynor <alex.gaynor@...il.com>,
	Wedson Almeida Filho <wedsonaf@...il.com>,
	Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Benno Lossin <benno.lossin@...ton.me>,
	Andreas Hindborg <a.hindborg@...sung.com>,
	Alice Ryhl <aliceryhl@...gle.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Andrea Parri <parri.andrea@...il.com>,
	Will Deacon <will@...nel.org>, Nicholas Piggin <npiggin@...il.com>,
	David Howells <dhowells@...hat.com>,
	Jade Alglave <j.alglave@....ac.uk>,
	Luc Maranget <luc.maranget@...ia.fr>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Akira Yokosawa <akiyks@...il.com>,
	Daniel Lustig <dlustig@...dia.com>,
	Joel Fernandes <joel@...lfernandes.org>,
	Nathan Chancellor <nathan@...nel.org>,
	Nick Desaulniers <ndesaulniers@...gle.com>,
	kent.overstreet@...il.com, elver@...gle.com,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Catalin Marinas <catalin.marinas@....com>,
	torvalds@...ux-foundation.org, linux-arm-kernel@...ts.infradead.org,
	linux-fsdevel@...r.kernel.org, Trevor Gross <tmgross@...ch.edu>,
	dakr@...hat.com
Subject: Re: [RFC 1/2] rust: Introduce atomic API helpers

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.