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
+the resources within a task's current cpuset. They form a nested
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.
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
+policy, are both filtered through that task's 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.
+node that is not allowed in the requesting task's 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
- Each task in the system is attached to a cpuset, via a pointer
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.
+ allowed in that task's cpuset.
- Calls to mbind and set_mempolicy are filtered to just
- those Memory Nodes allowed in that tasks cpuset.
+ those Memory Nodes allowed in that task's cpuset.
- The root cpuset contains all the systems CPUs and Memory
Nodes.
- For any cpuset, one can define child cpusets containing a subset
- The hierarchy of cpusets can be mounted at /dev/cpuset, for
browsing and manipulation from user space.
- A cpuset may be marked exclusive, which ensures that no other
- cpuset (except direct ancestors and descendents) may contain
+ cpuset (except direct ancestors and descendants) may contain
any overlapping CPUs or Memory Nodes.
- You can list all the tasks (by pid) attached to any cpuset.
- in init/main.c, to initialize the root cpuset at system boot.
- in fork and exit, to attach and detach a task from its cpuset.
- in sched_setaffinity, to mask the requested CPUs by what's
- allowed in that tasks cpuset.
+ allowed in that task's cpuset.
- in sched.c migrate_live_tasks(), to keep migrating tasks within
the CPUs allowed by their cpuset, if possible.
- in the mbind and set_mempolicy system calls, to mask the requested
- Memory Nodes by what's allowed in that tasks cpuset.
+ Memory Nodes by what's allowed in that task's cpuset.
- in page_alloc.c, to restrict memory to allowed nodes.
- in vmscan.c, to restrict page recovery to the current cpuset.
modifying cpusets is via this cpuset file system.
The /proc/<pid>/status file for each task has four added lines,
-displaying the tasks cpus_allowed (on which CPUs it may be scheduled)
+displaying the task's cpus_allowed (on which CPUs it may be scheduled)
and mems_allowed (on which Memory Nodes it may obtain memory),
in the two formats seen in the following example:
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?
- - mem_hardwall flag: is memory allocation hardwalled
- - memory_pressure: measure of how much paging pressure in cpuset
- - memory_spread_page flag: if set, spread page cache evenly on allowed nodes
- - memory_spread_slab flag: if set, spread slab cache evenly on allowed nodes
- - sched_load_balance flag: if set, load balance within CPUs on that cpuset
- - sched_relax_domain_level: the searching range when migrating tasks
+ - cpuset.cpus: list of CPUs in that cpuset
+ - cpuset.mems: list of Memory Nodes in that cpuset
+ - cpuset.memory_migrate flag: if set, move pages to cpusets nodes
+ - cpuset.cpu_exclusive flag: is cpu placement exclusive?
+ - cpuset.mem_exclusive flag: is memory placement exclusive?
+ - cpuset.mem_hardwall flag: is memory allocation hardwalled
+ - cpuset.memory_pressure: measure of how much paging pressure in cpuset
+ - cpuset.memory_spread_page flag: if set, spread page cache evenly on allowed nodes
+ - cpuset.memory_spread_slab flag: if set, spread slab cache evenly on allowed nodes
+ - cpuset.sched_load_balance flag: if set, load balance within CPUs on that cpuset
+ - cpuset.sched_relax_domain_level: the searching range when migrating tasks
In addition, the root cpuset only has the following file:
- - memory_pressure_enabled flag: compute memory_pressure?
+ - cpuset.memory_pressure_enabled flag: compute memory_pressure?
New cpusets are created using the mkdir system call or shell
command. The properties of a cpuset, such as its flags, allowed
--------------------------------
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
+a direct ancestor or descendant, may share any of the same CPUs or
Memory Nodes.
-A cpuset that is mem_exclusive *or* mem_hardwall is "hardwalled",
+A cpuset that is cpuset.mem_exclusive *or* cpuset.mem_hardwall is "hardwalled",
i.e. it restricts kernel allocations for page, buffer and other data
commonly shared by the kernel across multiple users. All cpusets,
whether hardwalled or not, restrict allocations of memory for user
---------------------------
There are two boolean flag files per cpuset that control where the
kernel allocates pages for the file system buffers and related in
-kernel data structures. They are called 'memory_spread_page' and
-'memory_spread_slab'.
+kernel data structures. They are called 'cpuset.memory_spread_page' and
+'cpuset.memory_spread_slab'.
-If the per-cpuset boolean flag file 'memory_spread_page' is set, then
+If the per-cpuset boolean flag file 'cpuset.memory_spread_page' is set, then
the kernel will spread the file system buffers (page cache) evenly
over all the nodes that the faulting task is allowed to use, instead
of preferring to put those pages on the node where the task is running.
-If the per-cpuset boolean flag file 'memory_spread_slab' is set,
+If the per-cpuset boolean flag file 'cpuset.memory_spread_slab' is set,
then the kernel will spread some file system related slab caches,
such as for inodes and dentries evenly over all the nodes that the
faulting task is allowed to use, instead of preferring to put those
By default, both kinds of memory spreading are off, and memory
pages are allocated on the node local to where the task is running,
-except perhaps as modified by the tasks NUMA mempolicy or cpuset
+except perhaps as modified by the task's NUMA mempolicy or cpuset
configuration, so long as sufficient free memory pages are available.
When new cpusets are created, they inherit the memory spread settings
of their parent.
Setting memory spreading causes allocations for the affected page
-or slab caches to ignore the tasks NUMA mempolicy and be spread
+or slab caches to ignore the task's NUMA mempolicy and be spread
instead. Tasks using mbind() or set_mempolicy() calls to set NUMA
mempolicies will not notice any change in these calls as a result of
-their containing tasks memory spread settings. If memory spreading
+their containing task's memory spread settings. If memory spreading
is turned off, then the currently specified NUMA mempolicy once again
applies to memory page allocations.
-Both 'memory_spread_page' and 'memory_spread_slab' are boolean flag
+Both 'cpuset.memory_spread_page' and 'cpuset.memory_spread_slab' are boolean flag
files. By default they contain "0", meaning that the feature is off
for that cpuset. If a "1" is written to that file, then that turns
the named feature on.
The implementation is simple.
-Setting the flag 'memory_spread_page' turns on a per-process flag
+Setting the flag 'cpuset.memory_spread_page' turns on a per-process flag
PF_SPREAD_PAGE for each task that is in that cpuset or subsequently
joins that cpuset. The page allocation calls for the page cache
is modified to perform an inline check for this PF_SPREAD_PAGE task
flag, and if set, a call to a new routine cpuset_mem_spread_node()
returns the node to prefer for the allocation.
-Similarly, setting 'memory_spread_slab' turns on the flag
+Similarly, setting 'cpuset.memory_spread_slab' turns on the flag
PF_SPREAD_SLAB, and appropriately marked slab caches will allocate
pages from the node returned by cpuset_mem_spread_node().
The cpuset_mem_spread_node() routine is also simple. It uses the
value of a per-task rotor cpuset_mem_spread_rotor to select the next
-node in the current tasks mems_allowed to prefer for the allocation.
+node in the current task's mems_allowed to prefer for the allocation.
This memory placement policy is also known (in other contexts) as
round-robin or interleave.
system overhead on those CPUs, including avoiding task load
balancing if that is not needed.
-When the per-cpuset flag "sched_load_balance" is enabled (the default
-setting), it requests that all the CPUs in that cpusets allowed 'cpus'
+When the per-cpuset flag "cpuset.sched_load_balance" is enabled (the default
+setting), it requests that all the CPUs in that cpusets allowed 'cpuset.cpus'
be contained in a single sched domain, ensuring that load balancing
can move a task (not otherwised pinned, as by sched_setaffinity)
from any CPU in that cpuset to any other.
-When the per-cpuset flag "sched_load_balance" is disabled, then the
+When the per-cpuset flag "cpuset.sched_load_balance" is disabled, then the
scheduler will avoid load balancing across the CPUs in that cpuset,
--except-- in so far as is necessary because some overlapping cpuset
has "sched_load_balance" enabled.
-So, for example, if the top cpuset has the flag "sched_load_balance"
+So, for example, if the top cpuset has the flag "cpuset.sched_load_balance"
enabled, then the scheduler will have one sched domain covering all
-CPUs, and the setting of the "sched_load_balance" flag in any other
+CPUs, and the setting of the "cpuset.sched_load_balance" flag in any other
cpusets won't matter, as we're already fully load balancing.
Therefore in the above two situations, the top cpuset flag
-"sched_load_balance" should be disabled, and only some of the smaller,
+"cpuset.sched_load_balance" should be disabled, and only some of the smaller,
child cpusets have this flag enabled.
When doing this, you don't usually want to leave any unpinned tasks in
the top cpuset that might use non-trivial amounts of CPU, as such tasks
may be artificially constrained to some subset of CPUs, depending on
-the particulars of this flag setting in descendent cpusets. Even if
+the particulars of this flag setting in descendant cpusets. Even if
such a task could use spare CPU cycles in some other CPUs, the kernel
scheduler might not consider the possibility of load balancing that
task to that underused CPU.
Of course, tasks pinned to a particular CPU can be left in a cpuset
-that disables "sched_load_balance" as those tasks aren't going anywhere
+that disables "cpuset.sched_load_balance" as those tasks aren't going anywhere
else anyway.
There is an impedance mismatch here, between cpusets and sched domains.
It is necessary for sched domains to be flat because load balancing
across partially overlapping sets of CPUs would risk unstable dynamics
that would be beyond our understanding. So if each of two partially
-overlapping cpusets enables the flag 'sched_load_balance', then we
+overlapping cpusets enables the flag 'cpuset.sched_load_balance', then we
form a single sched domain that is a superset of both. We won't move
a task to a CPU outside it cpuset, but the scheduler load balancing
code might waste some compute cycles considering that possibility.
This mismatch is why there is not a simple one-to-one relation
-between which cpusets have the flag "sched_load_balance" enabled,
+between which cpusets have the flag "cpuset.sched_load_balance" enabled,
and the sched domain configuration. If a cpuset enables the flag, it
will get balancing across all its CPUs, but if it disables the flag,
it will only be assured of no load balancing if no other overlapping
cpuset enables the flag.
-If two cpusets have partially overlapping 'cpus' allowed, and only
+If two cpusets have partially overlapping 'cpuset.cpus' allowed, and only
one of them has this flag enabled, then the other may find its
tasks only partially load balanced, just on the overlapping CPUs.
This is just the general case of the top_cpuset example given a few
1.7.1 sched_load_balance implementation details.
------------------------------------------------
-The per-cpuset flag 'sched_load_balance' defaults to enabled (contrary
+The per-cpuset flag 'cpuset.sched_load_balance' defaults to enabled (contrary
to most cpuset flags.) When enabled for a cpuset, the kernel will
ensure that it can load balance across all the CPUs in that cpuset
(makes sure that all the CPUs in the cpus_allowed of that cpuset are
in the same sched domain.)
-If two overlapping cpusets both have 'sched_load_balance' enabled,
+If two overlapping cpusets both have 'cpuset.sched_load_balance' enabled,
then they will be (must be) both in the same sched domain.
-If, as is the default, the top cpuset has 'sched_load_balance' enabled,
+If, as is the default, the top cpuset has 'cpuset.sched_load_balance' enabled,
then by the above that means there is a single sched domain covering
the whole system, regardless of any other cpuset settings.
The kernel commits to user space that it will avoid load balancing
where it can. It will pick as fine a granularity partition of sched
domains as it can while still providing load balancing for any set
-of CPUs allowed to a cpuset having 'sched_load_balance' enabled.
+of CPUs allowed to a cpuset having 'cpuset.sched_load_balance' enabled.
The internal kernel cpuset to scheduler interface passes from the
cpuset code to the scheduler code a partition of the load balanced
The cpuset code builds a new such partition and passes it to the
scheduler sched domain setup code, to have the sched domains rebuilt
as necessary, whenever:
- - the 'sched_load_balance' flag of a cpuset with non-empty CPUs changes,
+ - the 'cpuset.sched_load_balance' flag of a cpuset with non-empty CPUs changes,
- or CPUs come or go from a cpuset with this flag enabled,
- - or 'sched_relax_domain_level' value of a cpuset with non-empty CPUs
+ - or 'cpuset.sched_relax_domain_level' value of a cpuset with non-empty CPUs
and with this flag enabled changes,
- or a cpuset with non-empty CPUs and with this flag enabled is removed,
- or a cpu is offlined/onlined.
Of course it takes some searching cost to find movable tasks and/or
idle CPUs, the scheduler might not search all CPUs in the domain
-everytime. In fact, in some architectures, the searching ranges on
+every time. In fact, in some architectures, the searching ranges on
events are limited in the same socket or node where the CPU locates,
-while the load balance on tick searchs all.
+while the load balance on tick searches all.
For example, assume CPU Z is relatively far from CPU X. Even if CPU Z
is idle while CPU X and the siblings are busy, scheduler can't migrate
on the next tick. For some applications in special situation, waiting
1 tick may be too long.
-The 'sched_relax_domain_level' file allows you to request changing
+The 'cpuset.sched_relax_domain_level' file allows you to request changing
this searching range as you like. This file takes int value which
indicates size of searching range in levels ideally as follows,
otherwise initial value -1 that indicates the cpuset has no request.
can be changed using the relax_domain_level= boot parameter.
This file is per-cpuset and affect the sched domain where the cpuset
-belongs to. Therefore if the flag 'sched_load_balance' of a cpuset
-is disabled, then 'sched_relax_domain_level' have no effect since
+belongs to. Therefore if the flag 'cpuset.sched_load_balance' of a cpuset
+is disabled, then 'cpuset.sched_relax_domain_level' have no effect since
there is no sched domain belonging the cpuset.
If multiple cpusets are overlapping and hence they form a single sched
If a cpuset has its Memory Nodes modified, then for each task attached
to that cpuset, the next time that the kernel attempts to allocate
a page of memory for that task, the kernel will notice the change
-in the tasks cpuset, and update its per-task memory placement to
+in the task's cpuset, and update its per-task memory placement to
remain within the new cpusets memory placement. If the task was using
mempolicy MPOL_BIND, and the nodes to which it was bound overlap with
its new cpuset, then the task will continue to use whatever subset
of MPOL_BIND nodes are still allowed in the new cpuset. If the task
was using MPOL_BIND and now none of its MPOL_BIND nodes are allowed
in the new cpuset, then the task will be essentially treated as if it
-was MPOL_BIND bound to the new cpuset (even though its numa placement,
+was MPOL_BIND bound to the new cpuset (even though its NUMA placement,
as queried by get_mempolicy(), doesn't change). If a task is moved
-from one cpuset to another, then the kernel will adjust the tasks
+from one cpuset to another, then the kernel will adjust the task's
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 in that cpuset
+If a cpuset has its 'cpuset.cpus' modified, then each task in that cpuset
will have its allowed CPU placement changed immediately. Similarly,
-if a tasks pid is written to another cpusets 'tasks' file, then its
+if a task's pid is written to another cpusets 'cpuset.tasks' file, 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,
Normally, once a page is allocated (given a physical page
of main memory) then that page stays on whatever node it
was allocated, so long as it remains allocated, even if the
-cpusets memory placement policy 'mems' subsequently changes.
-If the cpuset flag file 'memory_migrate' is set true, then when
+cpusets memory placement policy 'cpuset.mems' subsequently changes.
+If the cpuset flag file 'cpuset.memory_migrate' is set true, then when
tasks are attached to that cpuset, any pages that task had
allocated to it on nodes in its previous cpuset are migrated
-to the tasks new cpuset. The relative placement of the page within
+to the task's new cpuset. The relative placement of the page within
the cpuset is preserved during these migration operations if possible.
For example if the page was on the second valid node of the prior cpuset
then the page will be placed on the second valid node of the new cpuset.
-Also if 'memory_migrate' is set true, then if that cpusets
-'mems' file is modified, pages allocated to tasks in that
-cpuset, that were on nodes in the previous setting of 'mems',
+Also if 'cpuset.memory_migrate' is set true, then if that cpuset's
+'cpuset.mems' file is modified, pages allocated to tasks in that
+cpuset, that were on nodes in the previous setting of 'cpuset.mems',
will be moved to nodes in the new setting of 'mems.'
-Pages that were not in the tasks prior cpuset, or in the cpusets
-prior 'mems' setting, will not be moved.
+Pages that were not in the task's prior cpuset, or in the cpuset's
+prior 'cpuset.mems' setting, will not be moved.
There is an exception to the above. If hotplug functionality is used
to remove all the CPUs that are currently assigned to a cpuset,
kernel internal allocations that must be satisfied, immediately.
The kernel may drop some request, in rare cases even panic, if a
GFP_ATOMIC alloc fails. If the request cannot be satisfied within
-the current tasks cpuset, then we relax the cpuset, and look for
+the current task's cpuset, then we relax the cpuset, and look for
memory anywhere we can find it. It's better to violate the cpuset
than stress the kernel.
cd /dev/cpuset
mkdir Charlie
cd Charlie
- /bin/echo 2-3 > cpus
- /bin/echo 1 > mems
+ /bin/echo 2-3 > cpuset.cpus
+ /bin/echo 1 > cpuset.mems
/bin/echo $$ > tasks
sh
# The subshell 'sh' is now running in cpuset Charlie
In this directory you can find several files:
# ls
-cpu_exclusive memory_migrate mems tasks
-cpus memory_pressure notify_on_release
-mem_exclusive memory_spread_page sched_load_balance
-mem_hardwall memory_spread_slab sched_relax_domain_level
+cpuset.cpu_exclusive cpuset.memory_spread_slab
+cpuset.cpus cpuset.mems
+cpuset.mem_exclusive cpuset.sched_load_balance
+cpuset.mem_hardwall cpuset.sched_relax_domain_level
+cpuset.memory_migrate notify_on_release
+cpuset.memory_pressure tasks
+cpuset.memory_spread_page
Reading them will give you information about the state of this cpuset:
the CPUs and Memory Nodes it can use, the processes that are using
the cpuset.
Set some flags:
-# /bin/echo 1 > cpu_exclusive
+# /bin/echo 1 > cpuset.cpu_exclusive
Add some cpus:
-# /bin/echo 0-7 > cpus
+# /bin/echo 0-7 > cpuset.cpus
Add some mems:
-# /bin/echo 0-7 > mems
+# /bin/echo 0-7 > cpuset.mems
Now attach your shell to this cpuset:
# /bin/echo $$ > tasks
This is the syntax to use when writing in the cpus or mems files
in cpuset directories:
-# /bin/echo 1-4 > cpus -> set cpus list to cpus 1,2,3,4
-# /bin/echo 1,2,3,4 > cpus -> set cpus list to cpus 1,2,3,4
+# /bin/echo 1-4 > cpuset.cpus -> set cpus list to cpus 1,2,3,4
+# /bin/echo 1,2,3,4 > cpuset.cpus -> set cpus list to cpus 1,2,3,4
+
+To add a CPU to a cpuset, write the new list of CPUs including the
+CPU to be added. To add 6 to the above cpuset:
+
+# /bin/echo 1-4,6 > cpuset.cpus -> set cpus list to cpus 1,2,3,4,6
+
+Similarly to remove a CPU from a cpuset, write the new list of CPUs
+without the CPU to be removed.
+
+To remove all the CPUs:
+
+# /bin/echo "" > cpuset.cpus -> clear cpus list
2.3 Setting flags
-----------------
The syntax is very simple:
-# /bin/echo 1 > cpu_exclusive -> set flag 'cpu_exclusive'
-# /bin/echo 0 > cpu_exclusive -> unset flag 'cpu_exclusive'
+# /bin/echo 1 > cpuset.cpu_exclusive -> set flag 'cpuset.cpu_exclusive'
+# /bin/echo 0 > cpuset.cpu_exclusive -> unset flag 'cpuset.cpu_exclusive'
2.4 Attaching processes
-----------------------
git://ftp.safe.ca / safe / jmp / linux-2.6 / blobdiff