view Documentation/cpusets.txt @ 452:c7ed6fe5dca0

kexec: dont initialise regions in reserve_memory()

There is no need to initialise efi_memmap_res and boot_param_res in
reserve_memory() for the initial xen domain as it is done in
machine_kexec_setup_resources() using values from the kexec hypercall.

Signed-off-by: Simon Horman <horms@verge.net.au>
author Keir Fraser <keir.fraser@citrix.com>
date Thu Feb 28 10:55:18 2008 +0000 (2008-02-28)
parents 831230e53067
line source
2 -------
4 Copyright (C) 2004 BULL SA.
5 Written by Simon.Derr@bull.net
7 Portions Copyright (c) 2004-2006 Silicon Graphics, Inc.
8 Modified by Paul Jackson <pj@sgi.com>
9 Modified by Christoph Lameter <clameter@sgi.com>
12 =========
14 1. Cpusets
15 1.1 What are cpusets ?
16 1.2 Why are cpusets needed ?
17 1.3 How are cpusets implemented ?
18 1.4 What are exclusive cpusets ?
19 1.5 What does notify_on_release do ?
20 1.6 What is memory_pressure ?
21 1.7 What is memory spread ?
22 1.8 How do I use cpusets ?
23 2. Usage Examples and Syntax
24 2.1 Basic Usage
25 2.2 Adding/removing cpus
26 2.3 Setting flags
27 2.4 Attaching processes
28 3. Questions
29 4. Contact
31 1. Cpusets
32 ==========
34 1.1 What are cpusets ?
35 ----------------------
37 Cpusets provide a mechanism for assigning a set of CPUs and Memory
38 Nodes to a set of tasks.
40 Cpusets constrain the CPU and Memory placement of tasks to only
41 the resources within a tasks current cpuset. They form a nested
42 hierarchy visible in a virtual file system. These are the essential
43 hooks, beyond what is already present, required to manage dynamic
44 job placement on large systems.
46 Each task has a pointer to a cpuset. Multiple tasks may reference
47 the same cpuset. Requests by a task, using the sched_setaffinity(2)
48 system call to include CPUs in its CPU affinity mask, and using the
49 mbind(2) and set_mempolicy(2) system calls to include Memory Nodes
50 in its memory policy, are both filtered through that tasks cpuset,
51 filtering out any CPUs or Memory Nodes not in that cpuset. The
52 scheduler will not schedule a task on a CPU that is not allowed in
53 its cpus_allowed vector, and the kernel page allocator will not
54 allocate a page on a node that is not allowed in the requesting tasks
55 mems_allowed vector.
57 User level code may create and destroy cpusets by name in the cpuset
58 virtual file system, manage the attributes and permissions of these
59 cpusets and which CPUs and Memory Nodes are assigned to each cpuset,
60 specify and query to which cpuset a task is assigned, and list the
61 task pids assigned to a cpuset.
64 1.2 Why are cpusets needed ?
65 ----------------------------
67 The management of large computer systems, with many processors (CPUs),
68 complex memory cache hierarchies and multiple Memory Nodes having
69 non-uniform access times (NUMA) presents additional challenges for
70 the efficient scheduling and memory placement of processes.
72 Frequently more modest sized systems can be operated with adequate
73 efficiency just by letting the operating system automatically share
74 the available CPU and Memory resources amongst the requesting tasks.
76 But larger systems, which benefit more from careful processor and
77 memory placement to reduce memory access times and contention,
78 and which typically represent a larger investment for the customer,
79 can benefit from explicitly placing jobs on properly sized subsets of
80 the system.
82 This can be especially valuable on:
84 * Web Servers running multiple instances of the same web application,
85 * Servers running different applications (for instance, a web server
86 and a database), or
87 * NUMA systems running large HPC applications with demanding
88 performance characteristics.
89 * Also cpu_exclusive cpusets are useful for servers running orthogonal
90 workloads such as RT applications requiring low latency and HPC
91 applications that are throughput sensitive
93 These subsets, or "soft partitions" must be able to be dynamically
94 adjusted, as the job mix changes, without impacting other concurrently
95 executing jobs. The location of the running jobs pages may also be moved
96 when the memory locations are changed.
98 The kernel cpuset patch provides the minimum essential kernel
99 mechanisms required to efficiently implement such subsets. It
100 leverages existing CPU and Memory Placement facilities in the Linux
101 kernel to avoid any additional impact on the critical scheduler or
102 memory allocator code.
105 1.3 How are cpusets implemented ?
106 ---------------------------------
108 Cpusets provide a Linux kernel mechanism to constrain which CPUs and
109 Memory Nodes are used by a process or set of processes.
111 The Linux kernel already has a pair of mechanisms to specify on which
112 CPUs a task may be scheduled (sched_setaffinity) and on which Memory
113 Nodes it may obtain memory (mbind, set_mempolicy).
115 Cpusets extends these two mechanisms as follows:
117 - Cpusets are sets of allowed CPUs and Memory Nodes, known to the
118 kernel.
119 - Each task in the system is attached to a cpuset, via a pointer
120 in the task structure to a reference counted cpuset structure.
121 - Calls to sched_setaffinity are filtered to just those CPUs
122 allowed in that tasks cpuset.
123 - Calls to mbind and set_mempolicy are filtered to just
124 those Memory Nodes allowed in that tasks cpuset.
125 - The root cpuset contains all the systems CPUs and Memory
126 Nodes.
127 - For any cpuset, one can define child cpusets containing a subset
128 of the parents CPU and Memory Node resources.
129 - The hierarchy of cpusets can be mounted at /dev/cpuset, for
130 browsing and manipulation from user space.
131 - A cpuset may be marked exclusive, which ensures that no other
132 cpuset (except direct ancestors and descendents) may contain
133 any overlapping CPUs or Memory Nodes.
134 Also a cpu_exclusive cpuset would be associated with a sched
135 domain.
136 - You can list all the tasks (by pid) attached to any cpuset.
138 The implementation of cpusets requires a few, simple hooks
139 into the rest of the kernel, none in performance critical paths:
141 - in init/main.c, to initialize the root cpuset at system boot.
142 - in fork and exit, to attach and detach a task from its cpuset.
143 - in sched_setaffinity, to mask the requested CPUs by what's
144 allowed in that tasks cpuset.
145 - in sched.c migrate_all_tasks(), to keep migrating tasks within
146 the CPUs allowed by their cpuset, if possible.
147 - in sched.c, a new API partition_sched_domains for handling
148 sched domain changes associated with cpu_exclusive cpusets
149 and related changes in both sched.c and arch/ia64/kernel/domain.c
150 - in the mbind and set_mempolicy system calls, to mask the requested
151 Memory Nodes by what's allowed in that tasks cpuset.
152 - in page_alloc.c, to restrict memory to allowed nodes.
153 - in vmscan.c, to restrict page recovery to the current cpuset.
155 In addition a new file system, of type "cpuset" may be mounted,
156 typically at /dev/cpuset, to enable browsing and modifying the cpusets
157 presently known to the kernel. No new system calls are added for
158 cpusets - all support for querying and modifying cpusets is via
159 this cpuset file system.
161 Each task under /proc has an added file named 'cpuset', displaying
162 the cpuset name, as the path relative to the root of the cpuset file
163 system.
165 The /proc/<pid>/status file for each task has two added lines,
166 displaying the tasks cpus_allowed (on which CPUs it may be scheduled)
167 and mems_allowed (on which Memory Nodes it may obtain memory),
168 in the format seen in the following example:
170 Cpus_allowed: ffffffff,ffffffff,ffffffff,ffffffff
171 Mems_allowed: ffffffff,ffffffff
173 Each cpuset is represented by a directory in the cpuset file system
174 containing the following files describing that cpuset:
176 - cpus: list of CPUs in that cpuset
177 - mems: list of Memory Nodes in that cpuset
178 - memory_migrate flag: if set, move pages to cpusets nodes
179 - cpu_exclusive flag: is cpu placement exclusive?
180 - mem_exclusive flag: is memory placement exclusive?
181 - tasks: list of tasks (by pid) attached to that cpuset
182 - notify_on_release flag: run /sbin/cpuset_release_agent on exit?
183 - memory_pressure: measure of how much paging pressure in cpuset
185 In addition, the root cpuset only has the following file:
186 - memory_pressure_enabled flag: compute memory_pressure?
188 New cpusets are created using the mkdir system call or shell
189 command. The properties of a cpuset, such as its flags, allowed
190 CPUs and Memory Nodes, and attached tasks, are modified by writing
191 to the appropriate file in that cpusets directory, as listed above.
193 The named hierarchical structure of nested cpusets allows partitioning
194 a large system into nested, dynamically changeable, "soft-partitions".
196 The attachment of each task, automatically inherited at fork by any
197 children of that task, to a cpuset allows organizing the work load
198 on a system into related sets of tasks such that each set is constrained
199 to using the CPUs and Memory Nodes of a particular cpuset. A task
200 may be re-attached to any other cpuset, if allowed by the permissions
201 on the necessary cpuset file system directories.
203 Such management of a system "in the large" integrates smoothly with
204 the detailed placement done on individual tasks and memory regions
205 using the sched_setaffinity, mbind and set_mempolicy system calls.
207 The following rules apply to each cpuset:
209 - Its CPUs and Memory Nodes must be a subset of its parents.
210 - It can only be marked exclusive if its parent is.
211 - If its cpu or memory is exclusive, they may not overlap any sibling.
213 These rules, and the natural hierarchy of cpusets, enable efficient
214 enforcement of the exclusive guarantee, without having to scan all
215 cpusets every time any of them change to ensure nothing overlaps a
216 exclusive cpuset. Also, the use of a Linux virtual file system (vfs)
217 to represent the cpuset hierarchy provides for a familiar permission
218 and name space for cpusets, with a minimum of additional kernel code.
220 The cpus file in the root (top_cpuset) cpuset is read-only.
221 It automatically tracks the value of cpu_online_map, using a CPU
222 hotplug notifier. If and when memory nodes can be hotplugged,
223 we expect to make the mems file in the root cpuset read-only
224 as well, and have it track the value of node_online_map.
227 1.4 What are exclusive cpusets ?
228 --------------------------------
230 If a cpuset is cpu or mem exclusive, no other cpuset, other than
231 a direct ancestor or descendent, may share any of the same CPUs or
232 Memory Nodes.
234 A cpuset that is cpu_exclusive has a scheduler (sched) domain
235 associated with it. The sched domain consists of all CPUs in the
236 current cpuset that are not part of any exclusive child cpusets.
237 This ensures that the scheduler load balancing code only balances
238 against the CPUs that are in the sched domain as defined above and
239 not all of the CPUs in the system. This removes any overhead due to
240 load balancing code trying to pull tasks outside of the cpu_exclusive
241 cpuset only to be prevented by the tasks' cpus_allowed mask.
243 A cpuset that is mem_exclusive restricts kernel allocations for
244 page, buffer and other data commonly shared by the kernel across
245 multiple users. All cpusets, whether mem_exclusive or not, restrict
246 allocations of memory for user space. This enables configuring a
247 system so that several independent jobs can share common kernel data,
248 such as file system pages, while isolating each jobs user allocation in
249 its own cpuset. To do this, construct a large mem_exclusive cpuset to
250 hold all the jobs, and construct child, non-mem_exclusive cpusets for
251 each individual job. Only a small amount of typical kernel memory,
252 such as requests from interrupt handlers, is allowed to be taken
253 outside even a mem_exclusive cpuset.
256 1.5 What does notify_on_release do ?
257 ------------------------------------
259 If the notify_on_release flag is enabled (1) in a cpuset, then whenever
260 the last task in the cpuset leaves (exits or attaches to some other
261 cpuset) and the last child cpuset of that cpuset is removed, then
262 the kernel runs the command /sbin/cpuset_release_agent, supplying the
263 pathname (relative to the mount point of the cpuset file system) of the
264 abandoned cpuset. This enables automatic removal of abandoned cpusets.
265 The default value of notify_on_release in the root cpuset at system
266 boot is disabled (0). The default value of other cpusets at creation
267 is the current value of their parents notify_on_release setting.
270 1.6 What is memory_pressure ?
271 -----------------------------
272 The memory_pressure of a cpuset provides a simple per-cpuset metric
273 of the rate that the tasks in a cpuset are attempting to free up in
274 use memory on the nodes of the cpuset to satisfy additional memory
275 requests.
277 This enables batch managers monitoring jobs running in dedicated
278 cpusets to efficiently detect what level of memory pressure that job
279 is causing.
281 This is useful both on tightly managed systems running a wide mix of
282 submitted jobs, which may choose to terminate or re-prioritize jobs that
283 are trying to use more memory than allowed on the nodes assigned them,
284 and with tightly coupled, long running, massively parallel scientific
285 computing jobs that will dramatically fail to meet required performance
286 goals if they start to use more memory than allowed to them.
288 This mechanism provides a very economical way for the batch manager
289 to monitor a cpuset for signs of memory pressure. It's up to the
290 batch manager or other user code to decide what to do about it and
291 take action.
293 ==> Unless this feature is enabled by writing "1" to the special file
294 /dev/cpuset/memory_pressure_enabled, the hook in the rebalance
295 code of __alloc_pages() for this metric reduces to simply noticing
296 that the cpuset_memory_pressure_enabled flag is zero. So only
297 systems that enable this feature will compute the metric.
299 Why a per-cpuset, running average:
301 Because this meter is per-cpuset, rather than per-task or mm,
302 the system load imposed by a batch scheduler monitoring this
303 metric is sharply reduced on large systems, because a scan of
304 the tasklist can be avoided on each set of queries.
306 Because this meter is a running average, instead of an accumulating
307 counter, a batch scheduler can detect memory pressure with a
308 single read, instead of having to read and accumulate results
309 for a period of time.
311 Because this meter is per-cpuset rather than per-task or mm,
312 the batch scheduler can obtain the key information, memory
313 pressure in a cpuset, with a single read, rather than having to
314 query and accumulate results over all the (dynamically changing)
315 set of tasks in the cpuset.
317 A per-cpuset simple digital filter (requires a spinlock and 3 words
318 of data per-cpuset) is kept, and updated by any task attached to that
319 cpuset, if it enters the synchronous (direct) page reclaim code.
321 A per-cpuset file provides an integer number representing the recent
322 (half-life of 10 seconds) rate of direct page reclaims caused by
323 the tasks in the cpuset, in units of reclaims attempted per second,
324 times 1000.
327 1.7 What is memory spread ?
328 ---------------------------
329 There are two boolean flag files per cpuset that control where the
330 kernel allocates pages for the file system buffers and related in
331 kernel data structures. They are called 'memory_spread_page' and
332 'memory_spread_slab'.
334 If the per-cpuset boolean flag file 'memory_spread_page' is set, then
335 the kernel will spread the file system buffers (page cache) evenly
336 over all the nodes that the faulting task is allowed to use, instead
337 of preferring to put those pages on the node where the task is running.
339 If the per-cpuset boolean flag file 'memory_spread_slab' is set,
340 then the kernel will spread some file system related slab caches,
341 such as for inodes and dentries evenly over all the nodes that the
342 faulting task is allowed to use, instead of preferring to put those
343 pages on the node where the task is running.
345 The setting of these flags does not affect anonymous data segment or
346 stack segment pages of a task.
348 By default, both kinds of memory spreading are off, and memory
349 pages are allocated on the node local to where the task is running,
350 except perhaps as modified by the tasks NUMA mempolicy or cpuset
351 configuration, so long as sufficient free memory pages are available.
353 When new cpusets are created, they inherit the memory spread settings
354 of their parent.
356 Setting memory spreading causes allocations for the affected page
357 or slab caches to ignore the tasks NUMA mempolicy and be spread
358 instead. Tasks using mbind() or set_mempolicy() calls to set NUMA
359 mempolicies will not notice any change in these calls as a result of
360 their containing tasks memory spread settings. If memory spreading
361 is turned off, then the currently specified NUMA mempolicy once again
362 applies to memory page allocations.
364 Both 'memory_spread_page' and 'memory_spread_slab' are boolean flag
365 files. By default they contain "0", meaning that the feature is off
366 for that cpuset. If a "1" is written to that file, then that turns
367 the named feature on.
369 The implementation is simple.
371 Setting the flag 'memory_spread_page' turns on a per-process flag
372 PF_SPREAD_PAGE for each task that is in that cpuset or subsequently
373 joins that cpuset. The page allocation calls for the page cache
374 is modified to perform an inline check for this PF_SPREAD_PAGE task
375 flag, and if set, a call to a new routine cpuset_mem_spread_node()
376 returns the node to prefer for the allocation.
378 Similarly, setting 'memory_spread_cache' turns on the flag
379 PF_SPREAD_SLAB, and appropriately marked slab caches will allocate
380 pages from the node returned by cpuset_mem_spread_node().
382 The cpuset_mem_spread_node() routine is also simple. It uses the
383 value of a per-task rotor cpuset_mem_spread_rotor to select the next
384 node in the current tasks mems_allowed to prefer for the allocation.
386 This memory placement policy is also known (in other contexts) as
387 round-robin or interleave.
389 This policy can provide substantial improvements for jobs that need
390 to place thread local data on the corresponding node, but that need
391 to access large file system data sets that need to be spread across
392 the several nodes in the jobs cpuset in order to fit. Without this
393 policy, especially for jobs that might have one thread reading in the
394 data set, the memory allocation across the nodes in the jobs cpuset
395 can become very uneven.
398 1.8 How do I use cpusets ?
399 --------------------------
401 In order to minimize the impact of cpusets on critical kernel
402 code, such as the scheduler, and due to the fact that the kernel
403 does not support one task updating the memory placement of another
404 task directly, the impact on a task of changing its cpuset CPU
405 or Memory Node placement, or of changing to which cpuset a task
406 is attached, is subtle.
408 If a cpuset has its Memory Nodes modified, then for each task attached
409 to that cpuset, the next time that the kernel attempts to allocate
410 a page of memory for that task, the kernel will notice the change
411 in the tasks cpuset, and update its per-task memory placement to
412 remain within the new cpusets memory placement. If the task was using
413 mempolicy MPOL_BIND, and the nodes to which it was bound overlap with
414 its new cpuset, then the task will continue to use whatever subset
415 of MPOL_BIND nodes are still allowed in the new cpuset. If the task
416 was using MPOL_BIND and now none of its MPOL_BIND nodes are allowed
417 in the new cpuset, then the task will be essentially treated as if it
418 was MPOL_BIND bound to the new cpuset (even though its numa placement,
419 as queried by get_mempolicy(), doesn't change). If a task is moved
420 from one cpuset to another, then the kernel will adjust the tasks
421 memory placement, as above, the next time that the kernel attempts
422 to allocate a page of memory for that task.
424 If a cpuset has its CPUs modified, then each task using that
425 cpuset does _not_ change its behavior automatically. In order to
426 minimize the impact on the critical scheduling code in the kernel,
427 tasks will continue to use their prior CPU placement until they
428 are rebound to their cpuset, by rewriting their pid to the 'tasks'
429 file of their cpuset. If a task had been bound to some subset of its
430 cpuset using the sched_setaffinity() call, and if any of that subset
431 is still allowed in its new cpuset settings, then the task will be
432 restricted to the intersection of the CPUs it was allowed on before,
433 and its new cpuset CPU placement. If, on the other hand, there is
434 no overlap between a tasks prior placement and its new cpuset CPU
435 placement, then the task will be allowed to run on any CPU allowed
436 in its new cpuset. If a task is moved from one cpuset to another,
437 its CPU placement is updated in the same way as if the tasks pid is
438 rewritten to the 'tasks' file of its current cpuset.
440 In summary, the memory placement of a task whose cpuset is changed is
441 updated by the kernel, on the next allocation of a page for that task,
442 but the processor placement is not updated, until that tasks pid is
443 rewritten to the 'tasks' file of its cpuset. This is done to avoid
444 impacting the scheduler code in the kernel with a check for changes
445 in a tasks processor placement.
447 Normally, once a page is allocated (given a physical page
448 of main memory) then that page stays on whatever node it
449 was allocated, so long as it remains allocated, even if the
450 cpusets memory placement policy 'mems' subsequently changes.
451 If the cpuset flag file 'memory_migrate' is set true, then when
452 tasks are attached to that cpuset, any pages that task had
453 allocated to it on nodes in its previous cpuset are migrated
454 to the tasks new cpuset. The relative placement of the page within
455 the cpuset is preserved during these migration operations if possible.
456 For example if the page was on the second valid node of the prior cpuset
457 then the page will be placed on the second valid node of the new cpuset.
459 Also if 'memory_migrate' is set true, then if that cpusets
460 'mems' file is modified, pages allocated to tasks in that
461 cpuset, that were on nodes in the previous setting of 'mems',
462 will be moved to nodes in the new setting of 'mems.'
463 Pages that were not in the tasks prior cpuset, or in the cpusets
464 prior 'mems' setting, will not be moved.
466 There is an exception to the above. If hotplug functionality is used
467 to remove all the CPUs that are currently assigned to a cpuset,
468 then the kernel will automatically update the cpus_allowed of all
469 tasks attached to CPUs in that cpuset to allow all CPUs. When memory
470 hotplug functionality for removing Memory Nodes is available, a
471 similar exception is expected to apply there as well. In general,
472 the kernel prefers to violate cpuset placement, over starving a task
473 that has had all its allowed CPUs or Memory Nodes taken offline. User
474 code should reconfigure cpusets to only refer to online CPUs and Memory
475 Nodes when using hotplug to add or remove such resources.
477 There is a second exception to the above. GFP_ATOMIC requests are
478 kernel internal allocations that must be satisfied, immediately.
479 The kernel may drop some request, in rare cases even panic, if a
480 GFP_ATOMIC alloc fails. If the request cannot be satisfied within
481 the current tasks cpuset, then we relax the cpuset, and look for
482 memory anywhere we can find it. It's better to violate the cpuset
483 than stress the kernel.
485 To start a new job that is to be contained within a cpuset, the steps are:
487 1) mkdir /dev/cpuset
488 2) mount -t cpuset none /dev/cpuset
489 3) Create the new cpuset by doing mkdir's and write's (or echo's) in
490 the /dev/cpuset virtual file system.
491 4) Start a task that will be the "founding father" of the new job.
492 5) Attach that task to the new cpuset by writing its pid to the
493 /dev/cpuset tasks file for that cpuset.
494 6) fork, exec or clone the job tasks from this founding father task.
496 For example, the following sequence of commands will setup a cpuset
497 named "Charlie", containing just CPUs 2 and 3, and Memory Node 1,
498 and then start a subshell 'sh' in that cpuset:
500 mount -t cpuset none /dev/cpuset
501 cd /dev/cpuset
502 mkdir Charlie
503 cd Charlie
504 /bin/echo 2-3 > cpus
505 /bin/echo 1 > mems
506 /bin/echo $$ > tasks
507 sh
508 # The subshell 'sh' is now running in cpuset Charlie
509 # The next line should display '/Charlie'
510 cat /proc/self/cpuset
512 In the future, a C library interface to cpusets will likely be
513 available. For now, the only way to query or modify cpusets is
514 via the cpuset file system, using the various cd, mkdir, echo, cat,
515 rmdir commands from the shell, or their equivalent from C.
517 The sched_setaffinity calls can also be done at the shell prompt using
518 SGI's runon or Robert Love's taskset. The mbind and set_mempolicy
519 calls can be done at the shell prompt using the numactl command
520 (part of Andi Kleen's numa package).
522 2. Usage Examples and Syntax
523 ============================
525 2.1 Basic Usage
526 ---------------
528 Creating, modifying, using the cpusets can be done through the cpuset
529 virtual filesystem.
531 To mount it, type:
532 # mount -t cpuset none /dev/cpuset
534 Then under /dev/cpuset you can find a tree that corresponds to the
535 tree of the cpusets in the system. For instance, /dev/cpuset
536 is the cpuset that holds the whole system.
538 If you want to create a new cpuset under /dev/cpuset:
539 # cd /dev/cpuset
540 # mkdir my_cpuset
542 Now you want to do something with this cpuset.
543 # cd my_cpuset
545 In this directory you can find several files:
546 # ls
547 cpus cpu_exclusive mems mem_exclusive tasks
549 Reading them will give you information about the state of this cpuset:
550 the CPUs and Memory Nodes it can use, the processes that are using
551 it, its properties. By writing to these files you can manipulate
552 the cpuset.
554 Set some flags:
555 # /bin/echo 1 > cpu_exclusive
557 Add some cpus:
558 # /bin/echo 0-7 > cpus
560 Now attach your shell to this cpuset:
561 # /bin/echo $$ > tasks
563 You can also create cpusets inside your cpuset by using mkdir in this
564 directory.
565 # mkdir my_sub_cs
567 To remove a cpuset, just use rmdir:
568 # rmdir my_sub_cs
569 This will fail if the cpuset is in use (has cpusets inside, or has
570 processes attached).
572 2.2 Adding/removing cpus
573 ------------------------
575 This is the syntax to use when writing in the cpus or mems files
576 in cpuset directories:
578 # /bin/echo 1-4 > cpus -> set cpus list to cpus 1,2,3,4
579 # /bin/echo 1,2,3,4 > cpus -> set cpus list to cpus 1,2,3,4
581 2.3 Setting flags
582 -----------------
584 The syntax is very simple:
586 # /bin/echo 1 > cpu_exclusive -> set flag 'cpu_exclusive'
587 # /bin/echo 0 > cpu_exclusive -> unset flag 'cpu_exclusive'
589 2.4 Attaching processes
590 -----------------------
592 # /bin/echo PID > tasks
594 Note that it is PID, not PIDs. You can only attach ONE task at a time.
595 If you have several tasks to attach, you have to do it one after another:
597 # /bin/echo PID1 > tasks
598 # /bin/echo PID2 > tasks
599 ...
600 # /bin/echo PIDn > tasks
603 3. Questions
604 ============
606 Q: what's up with this '/bin/echo' ?
607 A: bash's builtin 'echo' command does not check calls to write() against
608 errors. If you use it in the cpuset file system, you won't be
609 able to tell whether a command succeeded or failed.
611 Q: When I attach processes, only the first of the line gets really attached !
612 A: We can only return one error code per call to write(). So you should also
613 put only ONE pid.
615 4. Contact
616 ==========
618 Web: http://www.bullopensource.org/cpuset