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Diffstat (limited to 'Documentation/cpusets.txt')
| -rw-r--r-- | Documentation/cpusets.txt | 24 |
1 files changed, 4 insertions, 20 deletions
diff --git a/Documentation/cpusets.txt b/Documentation/cpusets.txt index f2c0a684293..ec9de6917f0 100644 --- a/Documentation/cpusets.txt +++ b/Documentation/cpusets.txt @@ -35,7 +35,8 @@ CONTENTS: ---------------------- Cpusets provide a mechanism for assigning a set of CPUs and Memory -Nodes to a set of tasks. +Nodes to a set of tasks. In this document "Memory Node" refers to +an on-line node that contains memory. Cpusets constrain the CPU and Memory placement of tasks to only the resources within a tasks current cpuset. They form a nested @@ -86,9 +87,6 @@ This can be especially valuable on: 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 @@ -131,8 +129,6 @@ 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. - 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 @@ -144,9 +140,6 @@ 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. - - 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.c, to restrict memory to allowed nodes. @@ -220,8 +213,8 @@ and name space for cpusets, with a minimum of additional kernel code. The cpus and mems files in the root (top_cpuset) cpuset are read-only. The cpus file automatically tracks the value of cpu_online_map using a CPU hotplug notifier, and the mems file -automatically tracks the value of node_online_map using the -cpuset_track_online_nodes() hook. +automatically tracks the value of node_states[N_MEMORY]--i.e., +nodes with memory--using the cpuset_track_online_nodes() hook. 1.4 What are exclusive cpusets ? @@ -231,15 +224,6 @@ 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 scheduler (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 balancing 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. - A cpuset that is mem_exclusive restricts kernel allocations for page, buffer and other data commonly shared by the kernel across multiple users. All cpusets, whether mem_exclusive or not, restrict |