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authorPaul Jackson <pj@sgi.com>2008-02-07 00:14:48 -0800
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2008-02-07 08:42:23 -0800
commit8f5aa26c75b7722e80c0c5c5bb833d41865d7019 (patch)
tree7f1b27938b2732a70b99a65e49e83f1a77ac6aa9
parent73507f335f406ff31ceb97b39fa76eaee00f4f26 (diff)
cpusets: update_cpumask documentation fix
Update cpuset documentation to match the October 2007 "Fix cpusets update_cpumask" changes that now apply changes to a cpusets 'cpus' allowed mask immediately to the cpus_allowed of the tasks in that cpuset. Signed-off-by: Paul Jackson <pj@sgi.com> Acked-by: Cliff Wickman <cpw@sgi.com> Cc: David Rientjes <rientjes@google.com> Cc: Paul Menage <menage@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--Documentation/cpusets.txt23
1 files changed, 8 insertions, 15 deletions
diff --git a/Documentation/cpusets.txt b/Documentation/cpusets.txt
index 141bef1c859..43db6fe1281 100644
--- a/Documentation/cpusets.txt
+++ b/Documentation/cpusets.txt
@@ -523,21 +523,14 @@ from one cpuset to another, then the kernel will adjust the tasks
memory placement, as above, the next time that the kernel attempts
to allocate a page of memory for that task.
-If a cpuset has its CPUs modified, then each task using that
-cpuset does _not_ change its behavior automatically. In order to
-minimize the impact on the critical scheduling code in the kernel,
-tasks will continue to use their prior CPU placement until they
-are rebound to their cpuset, by rewriting their pid to the 'tasks'
-file of their cpuset. If a task had been bound to some subset of its
-cpuset using the sched_setaffinity() call, and if any of that subset
-is still allowed in its new cpuset settings, then the task will be
-restricted to the intersection of the CPUs it was allowed on before,
-and its new cpuset CPU placement. If, on the other hand, there is
-no overlap between a tasks prior placement and its new cpuset CPU
-placement, then the task will be allowed to run on any CPU allowed
-in its new cpuset. If a task is moved from one cpuset to another,
-its CPU placement is updated in the same way as if the tasks pid is
-rewritten to the 'tasks' file of its current cpuset.
+If a cpuset has its 'cpus' modified, then each task in that cpuset
+will have its allowed CPU placement changed immediately. Similarly,
+if a tasks pid is written to a cpusets 'tasks' file, in either its
+current cpuset or another cpuset, then its allowed CPU placement is
+changed immediately. If such a task had been bound to some subset
+of its cpuset using the sched_setaffinity() call, the task will be
+allowed to run on any CPU allowed in its new cpuset, negating the
+affect of the prior sched_setaffinity() call.
In summary, the memory placement of a task whose cpuset is changed is
updated by the kernel, on the next allocation of a page for that task,