linux-kernel - Re: [PATCH v3 1/2] rust: add static_key

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Date: Thu, 27 Jun 2024 10:34:39 +0200
From: Alice Ryhl <aliceryhl@...gle.com>
To: Boqun Feng <boqun.feng@...il.com>
Cc: Steven Rostedt <rostedt@...dmis.org>, Masami Hiramatsu <mhiramat@...nel.org>, 
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, Peter Zijlstra <peterz@...radead.org>, 
	Josh Poimboeuf <jpoimboe@...nel.org>, Jason Baron <jbaron@...mai.com>, 
	Ard Biesheuvel <ardb@...nel.org>, 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>, 
	linux-trace-kernel@...r.kernel.org, rust-for-linux@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org, 
	Arnd Bergmann <arnd@...db.de>, 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>, "Peter Zijlstra (Intel)" <peterz@...radaed.org>, 
	Sean Christopherson <seanjc@...gle.com>, Uros Bizjak <ubizjak@...il.com>, 
	Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>, 
	Oliver Upton <oliver.upton@...ux.dev>, Mark Rutland <mark.rutland@....com>, 
	Ryan Roberts <ryan.roberts@....com>, Fuad Tabba <tabba@...gle.com>, 
	linux-arm-kernel@...ts.infradead.org, 
	Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt <palmer@...belt.com>, 
	Albert Ou <aou@...s.berkeley.edu>, Anup Patel <apatel@...tanamicro.com>, 
	Andrew Jones <ajones@...tanamicro.com>, Alexandre Ghiti <alexghiti@...osinc.com>, 
	Conor Dooley <conor.dooley@...rochip.com>, Samuel Holland <samuel.holland@...ive.com>, 
	linux-riscv@...ts.infradead.org, Huacai Chen <chenhuacai@...nel.org>, 
	WANG Xuerui <kernel@...0n.name>, Bibo Mao <maobibo@...ngson.cn>, 
	Tiezhu Yang <yangtiezhu@...ngson.cn>, Andrew Morton <akpm@...ux-foundation.org>, 
	Tianrui Zhao <zhaotianrui@...ngson.cn>, loongarch@...ts.linux.dev
Subject: Re: [PATCH v3 1/2] rust: add static_key_false

On Tue, Jun 25, 2024 at 6:18 PM Boqun Feng <boqun.feng@...il.com> wrote:
>
> Hi Alice,
>
> On Fri, Jun 21, 2024 at 10:35:26AM +0000, Alice Ryhl wrote:
> > Add just enough support for static key so that we can use it from
> > tracepoints. Tracepoints rely on `static_key_false` even though it is
> > deprecated, so we add the same functionality to Rust.
> >
> > It is not possible to use the existing C implementation of
> > arch_static_branch because it passes the argument `key` to inline
> > assembly as an 'i' parameter, so any attempt to add a C helper for this
> > function will fail to compile because the value of `key` must be known
> > at compile-time.
> >
> > Signed-off-by: Alice Ryhl <aliceryhl@...gle.com>
>
> [Add linux-arch, and related arch maintainers Cced]
>
> Since inline asms are touched here, please consider copying linux-arch
> and arch maintainers next time ;-)

Will do.

> For x86_64 and arm64 bits:
>
> Acked-by: Boqun Feng <boqun.feng@...il.com>
>
> One thing though, we should split the arch-specific impls into different
> files, for example: rust/kernel/arch/arm64.rs or rust/arch/arm64.rs.
> That'll be easier for arch maintainers to watch the Rust changes related
> to a particular architecture.

Is that how you would prefer to name these files? You don't want
static_key somewhere in the filename?

> Another thought is that, could you implement an arch_static_branch!()
> (instead of _static_key_false!()) and use it for static_key_false!()
> similar to what we have in C? The benefit is that at least for myself
> it'll be easier to compare the implementation between C and Rust.

I can try to include that.

Alice