On 10/12/23 15:23, Joseph Salisbury wrote:
On 10/12/23 15:10, Waiman Long wrote:
On 10/12/23 13:27, Joseph Salisbury wrote:
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?
Yes, the quoted description applies only to cpu controller. Even for
v1 cpu controller, the realtime support is problematic and there is
no easy solution to that. That is why cgroup v2 doesn't support it.
For other controllers, whether the processes are RT or not are
irrelevant. They are equally supported.
Cheers,
Longman
Thanks for the feedback, Longman!
One further tidbit is the fact that the deadline scheduling policy can
be used as a replacement of using cgroup v1 cpu controller RT knobs to
place a limit one how many RT tasks can run on a CPU.
Cheers,
Longman
