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authorCliff Wickman <cpw@sgi.com>2007-10-19 06:40:46 (GMT)
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-10-19 18:53:44 (GMT)
commit470fd646444c65a5d062a371f5ec8dcedee61239 (patch)
tree59b923486d4a95efa07c4b2ad7cb0b1fcc3f3c88 /Documentation/cpu-hotplug.txt
parentbd89aabc6761de1c35b154fe6f914a445d301510 (diff)
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 <cpw@sgi.com> Cc: Oleg Nesterov <oleg@tv-sign.ru> Cc: Christoph Lameter <clameter@sgi.com> Cc: Paul Jackson <pj@sgi.com> Cc: Ingo Molnar <mingo@elte.hu> Signed-off-by: Paul Jackson <pj@sgi.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation/cpu-hotplug.txt')
-rw-r--r--Documentation/cpu-hotplug.txt4
1 files changed, 3 insertions, 1 deletions
diff --git a/Documentation/cpu-hotplug.txt b/Documentation/cpu-hotplug.txt
index b6d24c2..a741f65 100644
--- a/Documentation/cpu-hotplug.txt
+++ b/Documentation/cpu-hotplug.txt
@@ -220,7 +220,9 @@ A: The following happen, listed in no particular order :-)
CPU_DOWN_PREPARE or CPU_DOWN_PREPARE_FROZEN, depending on whether or not the
CPU is being offlined while tasks are frozen due to a suspend operation in
progress
-- All process is migrated away from this outgoing CPU to a new CPU
+- All processes are migrated away from this outgoing CPU to new CPUs.
+ The new CPU is chosen from each process' current cpuset, which may be
+ a subset of all online CPUs.
- All interrupts targeted to this CPU is migrated to a new CPU
- timers/bottom half/task lets are also migrated to a new CPU
- Once all services are migrated, kernel calls an arch specific routine

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