Re: Question Regarding isolcpus

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

On 2023-09-26 12:45:14 [-0400], Joseph Salisbury wrote:
> Hi All,
Hi,

> I have a question regarding the isolcpus parameter.  I've been seeing this
> parameter commonly used. However, in the kernel.org documentation[0],
> isolcpus is listed as depreciated.
> 
> Is it the case that isolcpus should not be used at all?  I've seen it used
> in conjunction with taskset.  However, should we now be telling rt users to
> use only cpusets in cgroups?  I see that CPUAffinity can be set in
> /etc/systemd/system.conf.  Is that the preferred method, so the process
> scheduler will automatically migrate processes between the cpusets in the
> cgroup cpuset or the list set by CPUAffinity?

Frederic might know if there is an actual timeline to remove it. The
suggestions since then is to use cpusets which should be more flexible.
There was also some work (which went into v6.1 I think) to be able to
reconfigure the partitions at run-time while isolcpus= is a boot time
option.
From what I remember, you have a default/system cpuset which all tasks
use by default and then you can add another cpuset for the "isolated"
CPUs. Based on the partition it can be either the default one or
isolated [0]. The latter would exclude the CPUs from load balancing
which is what isolcpus= does.

[0] f28e22441f353 ("cgroup/cpuset: Add a new isolated cpus.partition type")

> Thanks,
> 
> Joe

Sebastian