schedutils/taskset.1.adoc

   1 //po4a: entry man manual
   2 ////
   3 taskset(1) manpage
   4 Copyright (C) 2004 Robert Love
   5
   6 This is free documentation; you can redistribute it and/or
   7 modify it under the terms of the GNU General Public License,
   8 version 2, as published by the Free Software Foundation.
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  10 The GNU General Public License's references to "object code"
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  13 intermediate and printed output.
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  15 This manual is distributed in the hope that it will be useful,
  16 but WITHOUT ANY WARRANTY; without even the implied warranty of
  17 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  18 GNU General Public License for more details.
  19
  20 You should have received a copy of the GNU General Public License along
  21 with this program; if not, write to the Free Software Foundation, Inc.,
  22 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  23 ////
  24 = taskset(1)
  25 :doctype: manpage
  26 :man manual: User Commands
  27 :man source: util-linux {release-version}
  28 :page-layout: base
  29 :command: taskset
  30 :colon: :
  31 :copyright: ©
  32
  33 == NAME
  34
  35 taskset - set or retrieve a process's CPU affinity
  36
  37 == SYNOPSIS
  38
  39 *taskset* [options] _mask command_ [_argument_...]
  40
  41 *taskset* [options] *-p* [_mask_] _pid_
  42
  43 == DESCRIPTION
  44
  45 The *taskset* command is used to set or retrieve the CPU affinity of a running process given its _pid_, or to launch a new _command_ with a given CPU affinity. CPU affinity is a scheduler property that "bonds" a process to a given set of CPUs on the system. The Linux scheduler will honor the given CPU affinity and the process will not run on any other CPUs. Note that the Linux scheduler also supports natural CPU affinity: the scheduler attempts to keep processes on the same CPU as long as practical for performance reasons. Therefore, forcing a specific CPU affinity is useful only in certain applications.   The affinity of some processes like kernel per-CPU threads cannot be set.
  46
  47 The CPU affinity is represented as a bitmask, with the lowest order bit corresponding to the first logical CPU and the highest order bit corresponding to the last logical CPU. Not all CPUs may exist on a given system but a mask may specify more CPUs than are present. A retrieved mask will reflect only the bits that correspond to CPUs physically on the system. If an invalid mask is given (i.e., one that corresponds to no valid CPUs on the current system) an error is returned. The masks may be specified in hexadecimal (with or without a leading "0x"), or as a CPU list with the *--cpu-list* option. For example,
  48
  49 *0x00000001*::
  50 is processor #0,
  51
  52 *0x00000003*::
  53 is processors #0 and #1,
  54
  55 *FFFFFFFF*::
  56 is processors #0 through #31,
  57
  58 *0x32*::
  59 is processors #1, #4, and #5,
  60
  61 *--cpu-list 0-2,6*::
  62 is processors #0, #1, #2, and #6.
  63
  64 *--cpu-list 0-10:2*::
  65 is processors #0, #2, #4, #6, #8 and #10. The suffix ":N" specifies stride in the range, for example 0-10:3 is interpreted as 0,3,6,9 list.
  66
  67 When *taskset* returns, it is guaranteed that the given program has been scheduled to a legal CPU.
  68
  69 == OPTIONS
  70
  71 *-a*, *--all-tasks*::
  72 Set or retrieve the CPU affinity of all the tasks (threads) for a given PID.
  73
  74 *-c*, *--cpu-list*::
  75 Interpret _mask_ as numerical list of processors instead of a bitmask. Numbers are separated by commas and may include ranges. For example: *0,5,8-11*.
  76
  77 *-p*, *--pid*::
  78 Operate on an existing PID and do not launch a new task.
  79
  80 include::man-common/help-version.adoc[]
  81
  82 == USAGE
  83
  84 //TRANSLATORS: Keep {colon} untranslated.
  85 The default behavior is to run a new command with a given affinity mask{colon}::
  86 *taskset* _mask_ _command_ [_arguments_]
  87
  88 //TRANSLATORS: Keep {colon} untranslated.
  89 You can also retrieve the CPU affinity of an existing task{colon}::
  90 *taskset -p* _pid_
  91
  92 //TRANSLATORS: Keep {colon} untranslated.
  93 Or set it{colon}::
  94 *taskset -p* _mask pid_
  95
  96 //TRANSLATORS: Keep {colon} untranslated.
  97 When a cpu-list is specified for an existing process, the *-p* and *-c* options must be grouped together{colon}::
  98 *taskset -pc* _cpu-list pid_
  99
 100 //TRANSLATORS: Keep {colon} untranslated.
 101 The *--cpu-list* form is applicable only for launching new commands{colon}::
 102 *taskset --cpu-list* _cpu-list command_
 103
 104 == PERMISSIONS
 105
 106 A user can change the CPU affinity of a process belonging to the same user. A user must possess *CAP_SYS_NICE* to change the CPU affinity of a process belonging to another user. A user can retrieve the affinity mask of any process.
 107
 108 == RETURN VALUE
 109
 110 *taskset* returns 0 in its affinity-getting mode as long as the provided PID exists.
 111
 112 *taskset* returns 0 in its affinity-setting mode as long as the underlying *sched_setaffinity*(2) system call does.  The success of the command does not guarantee that the specified thread has actually migrated to the indicated CPU(s), but only that the thread will not migrate to a CPU outside the new affinity mask.  For example, the affinity of the kernel thread kswapd can be set, but the thread may not immediately migrate and is not guaranteed to ever do so:
 113
 114 $ ps ax -o comm,psr,pid | grep kswapd +
 115 kswapd0           4      82 +
 116 $ sudo taskset -p 1 82 +
 117 pid 82's current affinity mask: 1 +
 118 pid 82's new affinity mask: 1 +
 119 $ echo $? +
 120 0 +
 121 $ ps ax -o comm,psr,pid | grep kswapd +
 122 kswapd0           4      82 +
 123 $ taskset -p 82 +
 124 pid 82's current affinity mask: 1 +
 125
 126 In contrast, when the user specifies an illegal affinity, taskset will print an error and return 1:
 127
 128 $ ps ax -o comm,psr,pid | grep ksoftirqd/0 +
 129 ksoftirqd/0       0      14 +
 130 $ sudo taskset -p 1 14 +
 131 pid 14's current affinity mask: 1 +
 132 taskset: failed to set pid 14's affinity: Invalid argument +
 133 $ echo $? +
 134 1 +
 135
 136 == AUTHORS
 137
 138 Written by Robert M. Love.
 139
 140 == COPYRIGHT
 141
 142 //TRANSLATORS: Keep {copyright} untranslated.
 143 Copyright {copyright} 2004 Robert M. Love. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 144
 145 == SEE ALSO
 146
 147 *chrt*(1),
 148 *nice*(1),
 149 *renice*(1),
 150 *sched_getaffinity*(2),
 151 *sched_setaffinity*(2)
 152
 153 See *sched*(7) for a description of the Linux scheduling scheme.
 154
 155 include::man-common/bugreports.adoc[]
 156
 157 include::man-common/footer.adoc[]
 158
 159 ifdef::translation[]
 160 include::man-common/translation.adoc[]
 161 endif::[]