On Wed, Oct 27, 2021 at 2:06 PM Waiman Long <longman@xxxxxxxxxx> wrote: > > > On 10/26/21 7:58 PM, Barry Song wrote: > >> I think Tejun is concerned about a change in the default behavior of > >> cpuset v1. > >> > >> There is a special v2 mode for cpuset that is enabled by the mount > >> option "cpuset_v2_mode". This causes the cpuset v1 to adopt some of the > >> v2 behavior. I introduced this v2 mode a while back to address, I think, > >> a similar concern. Could you try that to see if it is able to address > >> your problem? If not, you can make some code adjustment within the > >> framework of the v2 mode. As long as it is an opt-in, I think we are > >> open to further change. > > I am also able to reproduce on Ubuntu 21.04 LTS. > > > > all docker will be put in this cgroups and its child cgroups: > > /sys/fs/cgroup/cpuset/docker > > > > disabling and enabling SMT by: > > echo off > /sys/devices/system/cpu/smt/control > > echo on > /sys/devices/system/cpu/smt/control > > > > or unpluging and pluging CPUs by: > > echo 0 > /sys/devices/system/cpu/cpuX/online > > echo 1 > /sys/devices/system/cpu/cpuX/online > > > > then all docker images will lose some CPUs. > > > > So should we document the broken behaviours somewhere? > > Is the special cpuset_v2_mode mount option able to fix the issue? > > This mode is documented in > > Documentation/admin-guide/cgroup-v1/cpuset.rst: > > The cpuset.effective_cpus and cpuset.effective_mems files are > normally read-only copies of cpuset.cpus and cpuset.mems files > respectively. If the cpuset cgroup filesystem is mounted with the > special "cpuset_v2_mode" option, the behavior of these files will become > similar to the corresponding files in cpuset v2. In other words, hotplug > events will not change cpuset.cpus and cpuset.mems. Those events will > only affect cpuset.effective_cpus and cpuset.effective_mems which show > the actual cpus and memory nodes that are currently used by this cpuset. > See Documentation/admin-guide/cgroup-v2.rst for more information about > cpuset v2 behavior. > > Maybe we can make it more visible. Is it possible to make cpuset_v2_mode true in default? not quite sure if it will harm something. > > Cheers, > Longman Thanks Barry
