linux-kernel - Re: [PATCH] sched/nohz: Fix NOHZ imbalance by adding options for ILB CPU

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: <916176fe-ad43-9dd2-ed1c-6f05f838d491@gentwo.org>
Date: Thu, 28 Aug 2025 08:44:44 -0700 (PDT)
From: "Christoph Lameter (Ampere)" <cl@...two.org>
To: Valentin Schneider <vschneid@...hat.com>
cc: Adam Li <adamli@...amperecomputing.com>, mingo@...hat.com, 
    peterz@...radead.org, juri.lelli@...hat.com, vincent.guittot@...aro.org, 
    dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com, 
    mgorman@...e.de, frederic@...nel.org, linux-kernel@...r.kernel.org, 
    patches@...erecomputing.com
Subject: Re: [PATCH] sched/nohz: Fix NOHZ imbalance by adding options for
 ILB CPU

On Thu, 28 Aug 2025, Valentin Schneider wrote:

> > Yes, binding the threads to CPU can work around the performance
> > issue caused by load imbalance. Should we document that 'nohz_full' may cause
> > the scheduler load balancing not working well and CPU affinity is preferred?
> >
>
> Yeah I guess we could highlight that.

We need to make sure that the idle cpus are used when available and
needed. Otherwise the scheduler is buggy.

Such a load balancing action means that there is a cpu that is running
multiple processes. Therefore the timer interrrupt and the scheduler
processing is active on at least one cpu. We can therefore do something
about the situation.

The scheduler needs to move one of the processes onto the idle cpu.