linux-kernel - Re: [RFC PATCH 0/6] cpuset: Allow to modify isolcpus through cpuset

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Date:   Mon, 19 Jul 2021 15:57:28 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Waiman Long <llong@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, Tejun Heo <tj@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Alex Belits <abelits@...vell.com>,
        Nitesh Lal <nilal@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Nicolas Saenz <nsaenzju@...hat.com>,
        Christoph Lameter <cl@...two.de>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        Zefan Li <lizefan.x@...edance.com>, cgroups@...r.kernel.org
Subject: Re: [RFC PATCH 0/6] cpuset: Allow to modify isolcpus through cpuset

On Fri, Jul 16, 2021 at 02:02:50PM -0400, Waiman Long wrote:
> On 7/14/21 9:54 AM, Frederic Weisbecker wrote:
> > The fact that "isolcpus=" behaviour can't be modified at runtime is an
> > eternal source of discussion and debate opposing a useful feature against
> > a terrible interface.
> > 
> > I've long since tried to figure out a proper way to control this at
> > runtime using cpusets, which isn't easy as a boot time single cpumask
> > is difficult to map to a hierarchy of cpusets that can even overlap.
> 
> I have a cpuset patch that allow disabling of load balancing in a cgroup-v2
> setting:
> 
> https://lore.kernel.org/lkml/20210621184924.27493-1-longman@redhat.com/
> 
> The idea of cpuset partition is that there will be no overlap of cpus in
> different partitions. So there will be no confusion whether a cpu is
> load-balanced or not.

Oh ok I missed that, time for me to check your patchset.

Thanks!

> 
> > 
> > The idea here is to map the boot-set isolation behaviour to any cpuset
> > directory whose cpumask is a subset of "isolcpus=". I let you browse
> > for details on the last patch.
> > 
> > Note this is still WIP and half-baked, but I figured it's important to
> > validate the interface early.
> 
> Using different cpumasks for different isolated properties is the easy part.
> The hard part is to make different subsystems to change their behavior as
> the isolation masks change dynamically at run time. Currently, they check
> the housekeeping cpumask only at boot time or when certain events happen.
> 
> Cheers,
> Longman
> 
>