From 470fd646444c65a5d062a371f5ec8dcedee61239 Mon Sep 17 00:00:00 2001 From: Cliff Wickman Date: Thu, 18 Oct 2007 23:40:46 -0700 Subject: hotplug cpu: migrate a task within its cpuset When a cpu is disabled, move_task_off_dead_cpu() is called for tasks that have been running on that cpu. Currently, such a task is migrated: 1) to any cpu on the same node as the disabled cpu, which is both online and among that task's cpus_allowed 2) to any cpu which is both online and among that task's cpus_allowed It is typical of a multithreaded application running on a large NUMA system to have its tasks confined to a cpuset so as to cluster them near the memory that they share. Furthermore, it is typical to explicitly place such a task on a specific cpu in that cpuset. And in that case the task's cpus_allowed includes only a single cpu. This patch would insert a preference to migrate such a task to some cpu within its cpuset (and set its cpus_allowed to its entire cpuset). With this patch, migrate the task to: 1) to any cpu on the same node as the disabled cpu, which is both online and among that task's cpus_allowed 2) to any online cpu within the task's cpuset 3) to any cpu which is both online and among that task's cpus_allowed In order to do this, move_task_off_dead_cpu() must make a call to cpuset_cpus_allowed_locked(), a new subset of cpuset_cpus_allowed(), that will not block. (name change - per Oleg's suggestion) Calls are made to cpuset_lock() and cpuset_unlock() in migration_call() to set the cpuset mutex during the whole migrate_live_tasks() and migrate_dead_tasks() procedure. [akpm@linux-foundation.org: build fix] [pj@sgi.com: Fix indentation and spacing] Signed-off-by: Cliff Wickman Cc: Oleg Nesterov Cc: Christoph Lameter Cc: Paul Jackson Cc: Ingo Molnar Signed-off-by: Paul Jackson Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/cpuset.c | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-) (limited to 'kernel/cpuset.c') diff --git a/kernel/cpuset.c b/kernel/cpuset.c index fa31cb9f9898..50f5dc463688 100644 --- a/kernel/cpuset.c +++ b/kernel/cpuset.c @@ -1818,10 +1818,23 @@ cpumask_t cpuset_cpus_allowed(struct task_struct *tsk) cpumask_t mask; mutex_lock(&callback_mutex); + mask = cpuset_cpus_allowed_locked(tsk); + mutex_unlock(&callback_mutex); + + return mask; +} + +/** + * cpuset_cpus_allowed_locked - return cpus_allowed mask from a tasks cpuset. + * Must be called with callback_mutex held. + **/ +cpumask_t cpuset_cpus_allowed_locked(struct task_struct *tsk) +{ + cpumask_t mask; + task_lock(tsk); guarantee_online_cpus(task_cs(tsk), &mask); task_unlock(tsk); - mutex_unlock(&callback_mutex); return mask; } -- cgit v1.2.3