Peter Zijlstra wrote:
Correct, Ingo objected to the fastpath overhead. Could you please try the below patch which tries to address the issue differently.
Works great. Thanks Tested-by: Sachin Sant <sachinp@xxxxxxxxxx> Regards -Sachin
--- Subject: sched: Fix balance vs hotplug race From: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> Date: Wed Nov 25 13:31:39 CET 2009 Since (e761b77: cpu hotplug, sched: Introduce cpu_active_map and redo sched domain managment) we have cpu_active_mask which is suppose to rule scheduler migration and load-balancing, except it never did. The particular problem being solved here is a crash in try_to_wake_up() where select_task_rq() ends up selecting an offline cpu because select_task_rq_fair() trusts the sched_domain tree to reflect the current state of affairs, similarly select_task_rq_rt() trusts the root_domain. However, the sched_domains are updated from CPU_DEAD, which is after the cpu is taken offline and after stop_machine is done. Therefore it can race perfectly well with code assuming the domains are right. Cure this by building the domains from cpu_active_mask on CPU_DOWN_PREPARE.
-- --------------------------------- Sachin Sant IBM Linux Technology Center India Systems and Technology Labs Bangalore, India --------------------------------- -- To unsubscribe from this list: send the line "unsubscribe linux-next" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
