linux-kernel - Re: [PATCH v5 1/2] rust: add static_key

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Message-ID: <20240802093954.GH39708@noisy.programming.kicks-ass.net>
Date: Fri, 2 Aug 2024 11:39:54 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Alice Ryhl <aliceryhl@...gle.com>
Cc: Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
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	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, Arnd Bergmann <arnd@...db.de>,
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	Andrew Morton <akpm@...ux-foundation.org>,
	Tianrui Zhao <zhaotianrui@...ngson.cn>, loongarch@...ts.linux.dev,
	WANG Rui <wangrui@...ngson.cn>
Subject: Re: [PATCH v5 1/2] rust: add static_key_false

On Fri, Aug 02, 2024 at 09:31:27AM +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.
> 
> One disadvantage of this patch is that it introduces a fair amount of
> duplicated inline assembly. However, this is a limited and temporary
> situation:
> 
> 1. Most inline assembly has no reason to be duplicated like this. It is
>    only needed here due to the use of 'i' parameters.
> 
> 2. Alice will submit a patch along the lines of [1] that removes the
>    duplication. This will happen as a follow-up to this patch series.

You're talking about yourself in the 3rd person?

What's the rush, why not do it right first?