Re: [PATCH 1/2] cgroup/cpuset: Keep current cpus list if cpus affinity was explicitly set

[Valentin Schneider]

On 28/07/22 10:59, Waiman Long wrote:
> On 7/28/22 10:44, Michal Koutný wrote:
>> This should apply only to tasks that were extracted out of the root
>> cgroup, no? (OK, those are all processes practically.)
> The reset is done on all cgroups in a particular subtree. In the case of
> cgroup root, it is all the processes in the system.
>>

I've been briefly playing with this, tasks in the cgroup root don't seem
affected on my end (QEMU + buildroot + latest tip/sched/core):

  $ mount -t cgroup2 none /sys/fs/cgroup
  $ /root/loop.sh &
  $ PID=$!
  $ taskset -pc 2-3 $PID
  pid 177's current affinity list: 0-3
  pid 177's new affinity list: 2,3
  $ echo +cpuset > /sys/fs/cgroup/cgroup.subtree_control
  $ taskset -pc $PID
  pid 177's current affinity list: 2,3

However tasks extracted out as mentioned by Michal definitely are:

  $ mount -t cgroup2 none /sys/fs/cgroup
  $ /root/loop.sh &
  $ PID=$!
  $ taskset -pc 2-3 $PID
  pid 172's current affinity list: 0-3
  pid 172's new affinity list: 2,3
  $ mkdir /sys/fs/cgroup/foobar
  $ echo $PID > /sys/fs/cgroup/foobar/cgroup.procs
  $ taskset -pc $PID
  pid 172's current affinity list: 2,3
  $ echo +cpuset > /sys/fs/cgroup/cgroup.subtree_control
  $ taskset -pc $PID
  pid 172's current affinity list: 0-3

IIUC this is just what happens anytime a task gets migrated to a new
cpuset. Initially loop.sh remains attached to the root cpuset, and the echo
+cpuset migrates it to the /foobar one.

Does that match what you're seeing?