> I'm still not convinced that we don't want to make the change only for > powerpc systemx - x86 systems AFAIK don't hotplug like drunken sailors.
We do on amd64. We run Ubuntu as virtual machine guests and do allow hot-plugging CPUs. We do not have cgmanager installed. -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1392176 Title: mounts cgroups unconditionally which causes undesired effects with cpu hotplug Status in cgmanager package in Ubuntu: Confirmed Status in linux package in Ubuntu: Confirmed Status in systemd package in Ubuntu: Incomplete Bug description: == Comment: #0 - Preeti U. Murthy <preeti.mur...@in.ibm.com> - 2014-10-20 04:40:12 == ---Problem Description--- Systemd mounts cgroups explicitly every boot. Since the user had no say in it, undesired consequences are observed in reaction to cpu hotplug operations. Here is how. Systemd moves the tasks to the cgroup mounted by it. This cgroup automatically becomes the child of the root cgroup which is present by default. The children cgroups are not expected to remember their configured cpusets after hotplug operations in the kernel. Hence when cpus are taken offline and brought back online they are no longer used for load balancing of tasks and hence remain unused. This is an undesired consequence because the user had not even asked for cgroups to be mounted, yet is not able to use the full capacity of the system. Only when the user himself creates cgroup hierarchies, should he be exposed to the side effects of cpu hotplug on cpusets. Else all online cpus must be made available to him which is not happening since systemd mounts cgroups on every boot. Hence please revert this feature or provide an explaination as to why this is being done. ---uname output--- Linux tul181p1 3.16.0-18-generic #25-Ubuntu SMP Fri Sep 26 02:39:53 UTC 2014 ppc64le ppc64le ppc64le GNU/Linux Machine Type = Tuleta 8286-42A ---Debugger--- A debugger was configured, however the system did not enter into the debugger ---Steps to Reproduce--- $ taskset -p $$ $ 0-127 $ echo 0 > /sys/devices/system/cpu/cpu7/online $ taskset -p $$ $ 0-6,8-127 $ echo 1 > /sys/devices/system/cpu/cpu7/online $ taskset -p $$ $ 0-6,8-127 Userspace tool common name: systemd The userspace tool has the following bit modes: 64-bit Userspace rpm: systemd_208-8ubuntu8_ppc64el.deb Userspace tool obtained from project website: 208-8ubuntu8 To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/cgmanager/+bug/1392176/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
