On Tue, 23 Feb 2010, Miao Xie wrote: > > Cpu hotplug sets top_cpuset's cpus_allowed to cpu_active_mask by default, > > regardless of what was onlined or offlined. cpus_attach in the context of > > your patch (in cpuset_attach()) passes cpu_possible_mask to > > set_cpus_allowed_ptr() if the task is being attached to top_cpuset, my > > question was why don't we pass cpu_active_mask instead? In other words, I > > think we should do > > > > cpumask_copy(cpus_attach, cpu_active_mask); > > > > when attached to top_cpuset like my patch did. > > If we pass cpu_active_mask to set_cpus_allowed_ptr(), task->cpus_allowed just contains > the online cpus. In this way, if we do cpu hotplug(such as: online some cpu), we must > update cpus_allowed of all tasks in the top cpuset. > > But if we pass cpu_possible_mask, we needn't update cpus_allowed of all tasks in the > top cpuset. And when the kernel looks for a cpu for task to run, the kernel will use > cpu_active_mask to filter out offline cpus in task->cpus_allowed. Thus, it is safe. > That is terribly inconsistent between top_cpuset and all descendants; all other cpusets require that task->cpus_allowed be a subset of cpu_online_mask, including those descendants that allow all cpus (and all mems). -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>