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| author | Cliff Wickman <cpw@sgi.com> | 2007-10-19 08:40:46 +0200 |
|---|---|---|
| committer | Linus Torvalds <torvalds@woody.linux-foundation.org> | 2007-10-19 20:53:44 +0200 |
| commit | 470fd646444c65a5d062a371f5ec8dcedee61239 (patch) | |
| tree | 59b923486d4a95efa07c4b2ad7cb0b1fcc3f3c88 /Documentation/cpu-hotplug.txt | |
| parent | Control groups: Replace "cont" with "cgrp" and other misc renaming (diff) | |
| download | linux-470fd646444c65a5d062a371f5ec8dcedee61239.tar.xz linux-470fd646444c65a5d062a371f5ec8dcedee61239.zip | |
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.txt | 4 |
1 files changed, 3 insertions, 1 deletions
diff --git a/Documentation/cpu-hotplug.txt b/Documentation/cpu-hotplug.txt index b6d24c22274b..a741f658a3c9 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 |