Date: Sun, 16 Jun 2024 11:23:20 -0400
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: Boqun Feng <boqun.feng@...il.com>
Cc: Benno Lossin <benno.lossin@...ton.me>, 
	Miguel Ojeda <miguel.ojeda.sandonis@...il.com>, 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>, 
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	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 07:16:30AM -0700, Boqun Feng wrote:
> On Sun, Jun 16, 2024 at 05:51:07AM -0400, Kent Overstreet wrote:
> > On Sat, Jun 15, 2024 at 03:12:33PM -0700, Boqun Feng wrote:
> > > What's the issue of having AtomicI32 and AtomicI64 first then? We don't
> > > need to do 1 or 2 until the real users show up.
> > > 
> > > And I'd like also to point out that there are a few more trait bound
> > > designs needed for Atomic<T>, for example, Atomic<u32> and Atomic<i32>
> > > have different sets of API (no inc_unless_negative() for u32).
> > > 
> > > Don't make me wrong, I have no doubt we can handle this in the type
> > > system, but given the design work need, won't it make sense that we take
> > > baby steps on this? We can first introduce AtomicI32 and AtomicI64 which
> > > already have real users, and then if there are some values of generic
> > > atomics, we introduce them and have proper discussion on design.
> > > 
> > > To me, it's perfectly fine that Atomic{I32,I64} co-exist with Atomic<T>.
> > > What's the downside? A bit specific example would help me understand
> > > the real concern here.
> > 
> > Err, what?
> > 
> > Of course we want generic atomics, and we need that for properly
> > supporting cmpxchg.
> > 
> 
> Nope. Note this series only introduces the atomic types (atomic_ C
> APIs), but cmpxchg C APIs (no atomic_ prefix) are probably presented via
> a different API, where we need to make it easier to interact with normal
> types, and we may use generic there.
> 
> > Bogun, you've got all the rust guys pushing for doing this with
> > generics, I'm not sure why you're being stubborn here?
> 
> Hmm? Have you seen the email I replied to John, a broader Rust community
> seems doesn't appreciate the idea of generic atomics.

Apologies, I appear to have gotten things backwards in my pre-coffee
reading, I'll have to catch up on the whole thread :)

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