linux-kernel - Re: [PATCH] cgroup/rstat: move css_rstat

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] [day] [month] [year] [list]

Message-ID: <v572yf2qnle6ikxjb2ofvcmkuvpantmngrprrofd4kcia4xtld@uge7ti65njyj>
Date: Thu, 31 Jul 2025 17:26:28 +0200
From: Michal Koutný <mkoutny@...e.com>
To: Bertrand Wlodarczyk <bertrand.wlodarczyk@...el.com>
Cc: tj@...nel.org, hannes@...xchg.org, cgroups@...r.kernel.org, 
	linux-kernel@...r.kernel.org, shakeel.butt@...ux.dev, inwardvessel@...il.com
Subject: Re: [PATCH] cgroup/rstat: move css_rstat_lock outside cpu loop

On Tue, Jul 22, 2025 at 02:43:19PM +0200, Bertrand Wlodarczyk <bertrand.wlodarczyk@...el.com> wrote:
> By moving the lock outside the CPU loop, we reduce the frequency
> of costly lock acquisition.

So IIUC, mere acquisition is so costly that it dwarves actual holding
(flushing) as there are presumbly no updates collected.

As Shakeel wrote, there are reasons for not holding this lock for very
long (beside that being a general rule).

> This adjustment slightly improves performance in scenarios where
> multiple CPUs concurrently attempt to acquire the lock for
> the same css.

It means they can read cpu.stat more frequently but will they get any
fresher or more precise data? This is not clear to me, I understand why
this benchmark improves but does it represent some real world
improvement?

Thanks,
Michal

Download attachment "signature.asc" of type "application/pgp-signature" (229 bytes)