Merge master.kernel.org:/home/rmk/linux-2.6-arm-smp

[linux-2.6] / Documentation / cpusets.txt

diff --git a/Documentation/cpusets.txt b/Documentation/cpusets.txt
index 2f8f24eaefd9ac746f8a1e98b6e2c99abcc23b58..ad944c06031294cc35265d82ecf2a8fcc12586de 100644 (file)
--- a/Documentation/cpusets.txt
+++ b/Documentation/cpusets.txt
@@ -51,6 +51,14 @@ mems_allowed vector.
 
 If a cpuset is cpu or mem exclusive, no other cpuset, other than a direct
 ancestor or descendent, may share any of the same CPUs or Memory Nodes.
 
 If a cpuset is cpu or mem exclusive, no other cpuset, other than a direct
 ancestor or descendent, may share any of the same CPUs or Memory Nodes.

+A cpuset that is cpu exclusive has a sched domain associated with it.
+The sched domain consists of all cpus in the current cpuset that are not
+part of any exclusive child cpusets.
+This ensures that the scheduler load balacing code only balances
+against the cpus that are in the sched domain as defined above and not
+all of the cpus in the system. This removes any overhead due to
+load balancing code trying to pull tasks outside of the cpu exclusive
+cpuset only to be prevented by the tasks' cpus_allowed mask.

 
 User level code may create and destroy cpusets by name in the cpuset
 virtual file system, manage the attributes and permissions of these
 
 User level code may create and destroy cpusets by name in the cpuset
 virtual file system, manage the attributes and permissions of these


@@ -84,6 +92,9 @@ This can be especially valuable on:
       and a database), or
     * NUMA systems running large HPC applications with demanding
       performance characteristics.
       and a database), or
     * NUMA systems running large HPC applications with demanding
       performance characteristics.

+    * Also cpu_exclusive cpusets are useful for servers running orthogonal
+      workloads such as RT applications requiring low latency and HPC
+      applications that are throughput sensitive

 
 These subsets, or "soft partitions" must be able to be dynamically
 adjusted, as the job mix changes, without impacting other concurrently
 
 These subsets, or "soft partitions" must be able to be dynamically
 adjusted, as the job mix changes, without impacting other concurrently


@@ -125,6 +136,8 @@ Cpusets extends these two mechanisms as follows:
  - A cpuset may be marked exclusive, which ensures that no other
    cpuset (except direct ancestors and descendents) may contain
    any overlapping CPUs or Memory Nodes.
  - A cpuset may be marked exclusive, which ensures that no other
    cpuset (except direct ancestors and descendents) may contain
    any overlapping CPUs or Memory Nodes.

+   Also a cpu_exclusive cpuset would be associated with a sched
+   domain.

  - You can list all the tasks (by pid) attached to any cpuset.
 
 The implementation of cpusets requires a few, simple hooks
  - You can list all the tasks (by pid) attached to any cpuset.
 
 The implementation of cpusets requires a few, simple hooks


@@ -136,6 +149,9 @@ into the rest of the kernel, none in performance critical paths:
    allowed in that tasks cpuset.
  - in sched.c migrate_all_tasks(), to keep migrating tasks within
    the CPUs allowed by their cpuset, if possible.
    allowed in that tasks cpuset.
  - in sched.c migrate_all_tasks(), to keep migrating tasks within
    the CPUs allowed by their cpuset, if possible.

+ - in sched.c, a new API partition_sched_domains for handling
+   sched domain changes associated with cpu_exclusive cpusets
+   and related changes in both sched.c and arch/ia64/kernel/domain.c

  - in the mbind and set_mempolicy system calls, to mask the requested
    Memory Nodes by what's allowed in that tasks cpuset.
  - in page_alloc, to restrict memory to allowed nodes.
  - in the mbind and set_mempolicy system calls, to mask the requested
    Memory Nodes by what's allowed in that tasks cpuset.
  - in page_alloc, to restrict memory to allowed nodes.