linux-kernel - Re: [RFC 2/2] rust: sync: Add atomic support

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Date: Sun, 16 Jun 2024 11:32:31 -0400
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
Cc: Boqun Feng <boqun.feng@...il.com>, 
	Benno Lossin <benno.lossin@...ton.me>, Gary Guo <gary@...yguo.net>, 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>, Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	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>, Peter Zijlstra <peterz@...radead.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, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	elver@...gle.com, Mark Rutland <mark.rutland@....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 2/2] rust: sync: Add atomic support

On Sun, Jun 16, 2024 at 05:14:56PM +0200, Miguel Ojeda wrote:
> On Sun, Jun 16, 2024 at 4:16 PM Boqun Feng <boqun.feng@...il.com> wrote:
> >
> > Hmm? Have you seen the email I replied to John, a broader Rust community
> > seems doesn't appreciate the idea of generic atomics.
> 
> I don't think we can easily draw that conclusion from those download
> numbers / dependent crates.
> 
> portable-atomic may be more popular simply because it provides
> features for platforms the standard library does not. The interface
> being generic or not may have nothing to do with it. Or perhaps
> because it has a 1.x version, while the other doesn't, etc.
> 
> In fact, the atomic crate is essentially about providing `Atomic<T>`,
> so one could argue that all those downloads are precisely from people
> that want a generic atomic.
> 
> Moreover, I noticed portable-atomic's issue #1 in GitHub is,
> precisely, adding `Atomic<T>` support. The maintainer has a PR for
> that updated over time, most recently a few hours ago.
> 
> There is also `AtomicCell<T>` from crossbeam, which is the first
> feature listed in its docs.
> 
> Anyway...
> 
> The way I see it, both approaches seem similar (i.e. for what we are
> going to use them for today, at least) and neither apparently has a
> major downside today for those use cases (apart from needed refactors
> later to go to another approach).
> 
> (By the "generic approach", by the way, I mean just providing
> `Atomic<{i32,i64}>`, not a complex design)
> 
> So it is up to you on what you send for the non-RFC patches, of
> course, and if nobody has the time / wants to do the work for the
> "simple" generic approach, then we can just go ahead with this for the
> moment. But I think it would be nice to at least consider the "simple"
> generic approach to see how much worse it would be.
> 
> Other bits to consider, that perhaps give you arguments for one or the
> other: consequences on the compilation time, on inlining, on the error
> messages for new users, on the generated documentation, on how easy to
> grep they are, etc.

Yeah, rereading the thread - I'm with Miguel and Gary.

Generics are simply the correct way to do it, if the wider rust
community didn't do it that way I think that can be chalked up more to
historical baggage or needlessly copying the base integer type scheme.

Let's please do it right here, and generics are the correct approach.