linux-kernel - Re: [PATCH] select: core_sys_select add unlikely branch hint on return path

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Message-ID: <20250414-desolat-bauindustrie-7a705d36a1d0@brauner>
Date: Mon, 14 Apr 2025 12:04:41 +0200
From: Christian Brauner <brauner@...nel.org>
To: Colin Ian King <colin.i.king@...il.com>
Cc: Christian Brauner <brauner@...nel.org>,
	kernel-janitors@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Jan Kara <jack@...e.cz>,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] select: core_sys_select add unlikely branch hint on return path

On Mon, 14 Apr 2025 10:24:26 +0100, Colin Ian King wrote:
> Adding an unlikely() hint on the n < 0 comparison return path improves
> run-time performance of the select() system call, the negative
> value of n is very uncommon in normal select usage.
> 
> Benchmarking on an Debian based Intel(R) Core(TM) Ultra 9 285K with
> a 6.15-rc1 kernel built with 14.2.0 using a select of 1000 file
> descriptors with zero timeout shows a consistent call reduction from
> 258 ns down to 254 ns, which is a ~1.5% performance improvement.
> 
> [...]

Applied to the vfs-6.16.misc branch of the vfs/vfs.git tree.
Patches in the vfs-6.16.misc branch should appear in linux-next soon.

Please report any outstanding bugs that were missed during review in a
new review to the original patch series allowing us to drop it.

It's encouraged to provide Acked-bys and Reviewed-bys even though the
patch has now been applied. If possible patch trailers will be updated.

Note that commit hashes shown below are subject to change due to rebase,
trailer updates or similar. If in doubt, please check the listed branch.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
branch: vfs-6.16.misc

[1/1] select: core_sys_select add unlikely branch hint on return path
      https://git.kernel.org/vfs/vfs/c/7732f21402b5