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Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/cpusets.txt | 93 |
1 files changed, 43 insertions, 50 deletions
diff --git a/Documentation/cpusets.txt b/Documentation/cpusets.txt index ec9de6917f01..85eeab5e7e32 100644 --- a/Documentation/cpusets.txt +++ b/Documentation/cpusets.txt @@ -7,6 +7,7 @@ Written by Simon.Derr@bull.net Portions Copyright (c) 2004-2006 Silicon Graphics, Inc. Modified by Paul Jackson <pj@sgi.com> Modified by Christoph Lameter <clameter@sgi.com> +Modified by Paul Menage <menage@google.com> CONTENTS: ========= @@ -16,10 +17,9 @@ CONTENTS: 1.2 Why are cpusets needed ? 1.3 How are cpusets implemented ? 1.4 What are exclusive cpusets ? - 1.5 What does notify_on_release do ? - 1.6 What is memory_pressure ? - 1.7 What is memory spread ? - 1.8 How do I use cpusets ? + 1.5 What is memory_pressure ? + 1.6 What is memory spread ? + 1.7 How do I use cpusets ? 2. Usage Examples and Syntax 2.1 Basic Usage 2.2 Adding/removing cpus @@ -44,18 +44,19 @@ hierarchy visible in a virtual file system. These are the essential hooks, beyond what is already present, required to manage dynamic job placement on large systems. -Each task has a pointer to a cpuset. Multiple tasks may reference -the same cpuset. Requests by a task, using the sched_setaffinity(2) -system call to include CPUs in its CPU affinity mask, and using the -mbind(2) and set_mempolicy(2) system calls to include Memory Nodes -in its memory policy, are both filtered through that tasks cpuset, -filtering out any CPUs or Memory Nodes not in that cpuset. The -scheduler will not schedule a task on a CPU that is not allowed in -its cpus_allowed vector, and the kernel page allocator will not -allocate a page on a node that is not allowed in the requesting tasks -mems_allowed vector. - -User level code may create and destroy cpusets by name in the cpuset +Cpusets use the generic cgroup subsystem described in +Documentation/cgroup.txt. + +Requests by a task, using the sched_setaffinity(2) system call to +include CPUs in its CPU affinity mask, and using the mbind(2) and +set_mempolicy(2) system calls to include Memory Nodes in its memory +policy, are both filtered through that tasks cpuset, filtering out any +CPUs or Memory Nodes not in that cpuset. The scheduler will not +schedule a task on a CPU that is not allowed in its cpus_allowed +vector, and the kernel page allocator will not allocate a page on a +node that is not allowed in the requesting tasks mems_allowed vector. + +User level code may create and destroy cpusets by name in the cgroup virtual file system, manage the attributes and permissions of these cpusets and which CPUs and Memory Nodes are assigned to each cpuset, specify and query to which cpuset a task is assigned, and list the @@ -115,7 +116,7 @@ Cpusets extends these two mechanisms as follows: - Cpusets are sets of allowed CPUs and Memory Nodes, known to the kernel. - Each task in the system is attached to a cpuset, via a pointer - in the task structure to a reference counted cpuset structure. + in the task structure to a reference counted cgroup structure. - Calls to sched_setaffinity are filtered to just those CPUs allowed in that tasks cpuset. - Calls to mbind and set_mempolicy are filtered to just @@ -145,15 +146,10 @@ into the rest of the kernel, none in performance critical paths: - in page_alloc.c, to restrict memory to allowed nodes. - in vmscan.c, to restrict page recovery to the current cpuset. -In addition a new file system, of type "cpuset" may be mounted, -typically at /dev/cpuset, to enable browsing and modifying the cpusets -presently known to the kernel. No new system calls are added for -cpusets - all support for querying and modifying cpusets is via -this cpuset file system. - -Each task under /proc has an added file named 'cpuset', displaying -the cpuset name, as the path relative to the root of the cpuset file -system. +You should mount the "cgroup" filesystem type in order to enable +browsing and modifying the cpusets presently known to the kernel. No +new system calls are added for cpusets - all support for querying and +modifying cpusets is via this cpuset file system. The /proc/<pid>/status file for each task has two added lines, displaying the tasks cpus_allowed (on which CPUs it may be scheduled) @@ -163,16 +159,15 @@ in the format seen in the following example: Cpus_allowed: ffffffff,ffffffff,ffffffff,ffffffff Mems_allowed: ffffffff,ffffffff -Each cpuset is represented by a directory in the cpuset file system -containing the following files describing that cpuset: +Each cpuset is represented by a directory in the cgroup file system +containing (on top of the standard cgroup files) the following +files describing that cpuset: - cpus: list of CPUs in that cpuset - mems: list of Memory Nodes in that cpuset - memory_migrate flag: if set, move pages to cpusets nodes - cpu_exclusive flag: is cpu placement exclusive? - mem_exclusive flag: is memory placement exclusive? - - tasks: list of tasks (by pid) attached to that cpuset - - notify_on_release flag: run /sbin/cpuset_release_agent on exit? - memory_pressure: measure of how much paging pressure in cpuset In addition, the root cpuset only has the following file: @@ -237,21 +232,7 @@ such as requests from interrupt handlers, is allowed to be taken outside even a mem_exclusive cpuset. -1.5 What does notify_on_release do ? ------------------------------------- - -If the notify_on_release flag is enabled (1) in a cpuset, then whenever -the last task in the cpuset leaves (exits or attaches to some other -cpuset) and the last child cpuset of that cpuset is removed, then -the kernel runs the command /sbin/cpuset_release_agent, supplying the -pathname (relative to the mount point of the cpuset file system) of the -abandoned cpuset. This enables automatic removal of abandoned cpusets. -The default value of notify_on_release in the root cpuset at system -boot is disabled (0). The default value of other cpusets at creation -is the current value of their parents notify_on_release setting. - - -1.6 What is memory_pressure ? +1.5 What is memory_pressure ? ----------------------------- The memory_pressure of a cpuset provides a simple per-cpuset metric of the rate that the tasks in a cpuset are attempting to free up in @@ -308,7 +289,7 @@ the tasks in the cpuset, in units of reclaims attempted per second, times 1000. -1.7 What is memory spread ? +1.6 What is memory spread ? --------------------------- There are two boolean flag files per cpuset that control where the kernel allocates pages for the file system buffers and related in @@ -379,7 +360,7 @@ data set, the memory allocation across the nodes in the jobs cpuset can become very uneven. -1.8 How do I use cpusets ? +1.7 How do I use cpusets ? -------------------------- In order to minimize the impact of cpusets on critical kernel @@ -469,7 +450,7 @@ than stress the kernel. To start a new job that is to be contained within a cpuset, the steps are: 1) mkdir /dev/cpuset - 2) mount -t cpuset none /dev/cpuset + 2) mount -t cgroup -ocpuset cpuset /dev/cpuset 3) Create the new cpuset by doing mkdir's and write's (or echo's) in the /dev/cpuset virtual file system. 4) Start a task that will be the "founding father" of the new job. @@ -481,7 +462,7 @@ For example, the following sequence of commands will setup a cpuset named "Charlie", containing just CPUs 2 and 3, and Memory Node 1, and then start a subshell 'sh' in that cpuset: - mount -t cpuset none /dev/cpuset + mount -t cgroup -ocpuset cpuset /dev/cpuset cd /dev/cpuset mkdir Charlie cd Charlie @@ -513,7 +494,7 @@ Creating, modifying, using the cpusets can be done through the cpuset virtual filesystem. To mount it, type: -# mount -t cpuset none /dev/cpuset +# mount -t cgroup -o cpuset cpuset /dev/cpuset Then under /dev/cpuset you can find a tree that corresponds to the tree of the cpusets in the system. For instance, /dev/cpuset @@ -556,6 +537,18 @@ To remove a cpuset, just use rmdir: This will fail if the cpuset is in use (has cpusets inside, or has processes attached). +Note that for legacy reasons, the "cpuset" filesystem exists as a +wrapper around the cgroup filesystem. + +The command + +mount -t cpuset X /dev/cpuset + +is equivalent to + +mount -t cgroup -ocpuset X /dev/cpuset +echo "/sbin/cpuset_release_agent" > /dev/cpuset/release_agent + 2.2 Adding/removing cpus ------------------------ |