On 9/28/23 04:39, Sebastian Andrzej Siewior wrote:
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")
This question may be for the cgroups folks. The kernel.org
documentation has a WARNING which states: "cgroup2 doesn't yet support
control of realtime processes and the cpu controller can only be enabled
when all RT processes are in the root cgroup "[0]. Does this mean
real-time processes are only supported on cgroupsV1?
Also, this warning is stated for the "CPU" Controller, but there is no
mention of this for a "cpuset" controller. Does this imply that
real-time processes are supported with "cpuset" controllers?
Thanks,
Joe
[0]
https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v2.html#controllers
Thanks,
Joe
Sebastian
