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

From: Frederic Weisbecker
Date: Mon Jul 19 2021 - 09:57:33 EST

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:
> 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.


> >
> > 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