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

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Message-ID: <ZmxUxaIwHWnB42h-@Boquns-Mac-mini.home>
Date: Fri, 14 Jun 2024 07:33:41 -0700
From: Boqun Feng <boqun.feng@...il.com>
To: Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
Cc: 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>,
	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>,
	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 Fri, Jun 14, 2024 at 11:59:58AM +0200, Miguel Ojeda wrote:
> On Thu, Jun 13, 2024 at 9:05 PM Boqun Feng <boqun.feng@...il.com> wrote:
> >
> > Does this make sense?
> 
> Implementation-wise, if you think it is simpler or more clear/elegant
> to have the extra lower level layer, then that sounds fine.
> 
> However, I was mainly talking about what we would eventually expose to
> users, i.e. do we want to provide `Atomic<T>` to begin with? If yes,

The truth is I don't know ;-) I don't have much data on which one is
better. Personally, I think AtomicI32 and AtomicI64 make the users have
to think about size, alignment, etc, and I think that's important for
atomic users and people who review their code, because before one uses
atomics, one should ask themselves: why don't I use a lock? Atomics
provide the ablities to do low level stuffs and when doing low level
stuffs, you want to be more explicit than ergonomic.

That said, I keep an open mind on `Atomic<T>`, maybe it will show its
value at last. But right now, I'm not convinced personally.

> then we could make the lower layer private already.
> 
> We can defer that extra layer/work if needed even if we go for
> `Atomic<T>`, but it would be nice to understand if we have consensus
> for an eventual user-facing API, or if someone has any other opinion
> or concerns on one vs. the other.
> 

Yes, that'll be great. I'd love to see others' inputs!

Regards,
Boqun

> Cheers,
> Miguel