Hi Tejun, On Thu, Mar 26, 2020 at 03:20:35PM -0400, Tejun Heo wrote: > On Thu, Mar 26, 2020 at 03:16:23PM -0400, Joel Fernandes (Google) wrote: > > This deliberately changes the behavior of the per-cpuset > > cpus file to not be effected by hotplug. When a cpu is offlined, > > it will be removed from the cpuset/cpus file. When a cpu is onlined, > > if the cpuset originally requested that that cpu was part of the cpuset, > > that cpu will be restored to the cpuset. The cpus files still > > have to be hierachical, but the ranges no longer have to be out of > > the currently online cpus, just the physically present cpus. > > This is already the behavior on cgroup2 and I don't think we want to > introduce this big a behavior change to cgroup1 cpuset at this point. It is not really that big a change. Please go over the patch, we are not changing anything with how ->cpus_allowed works and interacts with the rest of the system and the scheduler. We have just introduced a new mask to keep track of which CPUs were requested without them being affected by hotplug. On CPU onlining, we restore the state of ->cpus_allowed as not be affected by hotplug. There's 3 companies that have this issue so that should tell you something. We don't want to carry this patch forever. Many people consider the hotplug behavior to be completely broken. thanks, - Joel
