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hotplug cpu: migrate a task within its cpuset

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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>
This commit is contained in:
Cliff Wickman
2007-10-18 23:40:46 -07:00
committed by Linus Torvalds
parent bd89aabc67
commit 470fd64644
4 changed files with 33 additions and 3 deletions
Download Patch File Download Diff File Expand all files Collapse all files

15
kernel/cpuset.c
View File

@@ -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;
}