linux-kernel - Re: [PATCH net-next] rust: net::phy inline if expressions to improve read

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <d1fe6fa4-da50-4899-8e2c-0721851c4e0d@lunn.ch>
Date: Fri, 19 Sep 2025 14:54:40 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Thorsten Blum <thorsten.blum@...ux.dev>
Cc: FUJITA Tomonori <fujita.tomonori@...il.com>,
	Trevor Gross <tmgross@...ch.edu>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Russell King <linux@...linux.org.uk>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Miguel Ojeda <ojeda@...nel.org>,
	Alex Gaynor <alex.gaynor@...il.com>,
	Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Benno Lossin <lossin@...nel.org>,
	Andreas Hindborg <a.hindborg@...nel.org>,
	Alice Ryhl <aliceryhl@...gle.com>,
	Danilo Krummrich <dakr@...nel.org>, netdev@...r.kernel.org,
	rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next] rust: net::phy inline if expressions to improve
 read_status

On Fri, Sep 19, 2025 at 01:20:08PM +0200, Thorsten Blum wrote:
> Inline the if expressions for dev.set_speed() and dev.set_duplex() to
> improve read_status(). This ensures dev.set_speed() is called only once

What is the issue of calling it twice, or 42 times??

> and allows us to remove the local variable 'duplex'.

And what is wrong with local variables?

And did you disassemble the code? What is the compiler actually doing?
Does it actually have a stack variable, or is it just a register? Does
the optimiser end up with just a single call to set_speed()?

This is slow path code. It gets called at most once per
second. Performance does not matter. Which means readability has much
higher preference. And i find the older version much easier to read.

	Andrew