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SCHED(7)		   Linux Programmer's Manual		      SCHED(7)

       sched - overview of CPU scheduling

       Since  Linux 2.6.23, the default scheduler is CFS, the "Completely Fair
       Scheduler".  The CFS scheduler replaced the earlier "O(1)" scheduler.

   API summary
       Linux provides the following  system  calls  for	 controlling  the  CPU
       scheduling  behavior,  policy, and priority of processes (or, more pre-
       cisely, threads).

	      Set a new nice value for the calling thread, and return the  new
	      nice value.

	      Return  the  nice value of a thread, a process group, or the set
	      of threads owned by a specified user.

	      Set the nice value of a thread, a process group, or the  set  of
	      threads owned by a specified user.

	      Set the scheduling policy and parameters of a specified thread.

	      Return the scheduling policy of a specified thread.

	      Set the scheduling parameters of a specified thread.

	      Fetch the scheduling parameters of a specified thread.

	      Return  the maximum priority available in a specified scheduling

	      Return the minimum priority available in a specified  scheduling

	      Fetch  the quantum used for threads that are scheduled under the
	      "round-robin" scheduling policy.

	      Cause the caller to relinquish  the  CPU,	 so  that  some	 other
	      thread be executed.

	      (Linux-specific) Set the CPU affinity of a specified thread.

	      (Linux-specific) Get the CPU affinity of a specified thread.

	      Set  the scheduling policy and parameters of a specified thread.
	      This (Linux-specific) system call provides  a  superset  of  the
	      functionality of sched_setscheduler(2) and sched_setparam(2).

	      Fetch  the  scheduling  policy  and  parameters  of  a specified
	      thread.  This (Linux-specific) system call provides  a  superset
	      of  the  functionality  of  sched_getscheduler(2) and sched_get-

   Scheduling policies
       The scheduler is the  kernel  component	that  decides  which  runnable
       thread will be executed by the CPU next.	 Each thread has an associated
       scheduling policy and a	static	scheduling  priority,  sched_priority.
       The  scheduler makes its decisions based on knowledge of the scheduling
       policy and static priority of all threads on the system.

       For threads scheduled under  one	 of  the  normal  scheduling  policies
       (SCHED_OTHER,  SCHED_IDLE,  SCHED_BATCH), sched_priority is not used in
       scheduling decisions (it must be specified as 0).

       Processes scheduled under one of the  real-time	policies  (SCHED_FIFO,
       SCHED_RR)  have	a  sched_priority  value  in  the  range 1 (low) to 99
       (high).	(As the numbers imply, real-time threads  always  have	higher
       priority	 than  normal threads.)	 Note well: POSIX.1 requires an imple-
       mentation to support only a minimum 32 distinct priority levels for the
       real-time  policies, and some systems supply just this minimum.	Porta-
       ble programs should use sched_get_priority_min(2) and  sched_get_prior-
       ity_max(2)  to  find the range of priorities supported for a particular

       Conceptually, the scheduler maintains a list of	runnable  threads  for
       each possible sched_priority value.  In order to determine which thread
       runs next, the scheduler looks for the nonempty list with  the  highest
       static priority and selects the thread at the head of this list.

       A  thread's scheduling policy determines where it will be inserted into
       the list of threads with equal static priority and  how	it  will  move
       inside this list.

       All scheduling is preemptive: if a thread with a higher static priority
       becomes ready to run, the currently running thread  will	 be  preempted
       and  returned  to  the  wait  list  for its static priority level.  The
       scheduling policy determines the	 ordering  only	 within	 the  list  of
       runnable threads with equal static priority.

   SCHED_FIFO: First in-first out scheduling
       SCHED_FIFO can be used only with static priorities higher than 0, which
       means that when a SCHED_FIFO threads becomes runnable, it  will	always
       immediately  preempt any currently running SCHED_OTHER, SCHED_BATCH, or
       SCHED_IDLE thread.  SCHED_FIFO is a simple scheduling algorithm without
       time  slicing.	For threads scheduled under the SCHED_FIFO policy, the
       following rules apply:

       *  A SCHED_FIFO thread that has been preempted  by  another  thread  of
	  higher  priority  will stay at the head of the list for its priority
	  and will resume execution as soon as all threads of higher  priority
	  are blocked again.

       *  When	a  SCHED_FIFO  thread becomes runnable, it will be inserted at
	  the end of the list for its priority.

       *  A   call    to    sched_setscheduler(2),    sched_setparam(2),    or
	  sched_setattr(2)  will put the SCHED_FIFO (or SCHED_RR) thread iden-
	  tified by pid at the start of the list if it	was  runnable.	 As  a
	  consequence,	it  may preempt the currently running thread if it has
	  the same priority.  (POSIX.1 specifies that the thread should go  to
	  the end of the list.)

       *  A thread calling sched_yield(2) will be put at the end of the list.

       No  other events will move a thread scheduled under the SCHED_FIFO pol-
       icy in the wait list of runnable threads with equal static priority.

       A SCHED_FIFO thread runs until either it is blocked by an I/O  request,
       it   is	 preempted   by	  a   higher  priority	thread,	 or  it	 calls

   SCHED_RR: Round-robin scheduling
       SCHED_RR is a simple enhancement of SCHED_FIFO.	 Everything  described
       above  for SCHED_FIFO also applies to SCHED_RR, except that each thread
       is allowed to run only for a  maximum  time  quantum.   If  a  SCHED_RR
       thread  has  been running for a time period equal to or longer than the
       time quantum, it will be put at the end of the list for	its  priority.
       A  SCHED_RR  thread that has been preempted by a higher priority thread
       and subsequently resumes execution as a running	thread	will  complete
       the  unexpired  portion of its round-robin time quantum.	 The length of
       the time quantum can be retrieved using sched_rr_get_interval(2).

   SCHED_DEADLINE: Sporadic task model deadline scheduling
       Since  version  3.14,  Linux  provides  a  deadline  scheduling	policy
       (SCHED_DEADLINE).   This	 policy	 is  currently	implemented using GEDF
       (Global Earliest Deadline First)	 in  conjunction  with	CBS  (Constant
       Bandwidth  Server).   To	 set  and  fetch  this	policy	and associated
       attributes,  one	 must  use  the	 Linux-specific	 sched_setattr(2)  and
       sched_getattr(2) system calls.

       A  sporadic  task is one that has a sequence of jobs, where each job is
       activated at most once per period.  Each job also has a relative	 dead-
       line,  before which it should finish execution, and a computation time,
       which is the CPU time necessary for executing the job.  The moment when
       a  task	wakes  up  because  a new job has to be executed is called the
       arrival time (also referred to as the request time  or  release	time).
       The  start  time is the time at which a task starts its execution.  The
       absolute deadline is thus obtained by adding the relative  deadline  to
       the arrival time.

       The following diagram clarifies these terms:

	   arrival/wakeup		     absolute deadline
		|    start time			   |
		|	 |			   |
		v	 v			   v
			 |<- comp. time ->|
		|<------- relative deadline ------>|
		|<-------------- period ------------------->|

       When   setting	a   SCHED_DEADLINE   policy   for   a	thread	 using
       sched_setattr(2), one can specify three parameters: Runtime,  Deadline,
       and  Period.   These  parameters	 do  not necessarily correspond to the
       aforementioned terms: usual practice is to  set	Runtime	 to  something
       bigger  than the average computation time (or worst-case execution time
       for hard real-time tasks),  Deadline  to	 the  relative	deadline,  and
       Period to the period of the task.  Thus, for SCHED_DEADLINE scheduling,
       we have:

	   arrival/wakeup		     absolute deadline
		|    start time			   |
		|	 |			   |
		v	 v			   v
			 |<-- Runtime ------->|
		|<----------- Deadline ----------->|
		|<-------------- Period ------------------->|

       The three deadline-scheduling parameters correspond to  the  sched_run-
       time,  sched_deadline, and sched_period fields of the sched_attr struc-
       ture; see sched_setattr(2).  These fields express  values  in  nanosec-
       onds.   If  sched_period is specified as 0, then it is made the same as

       The kernel requires that:

	   sched_runtime <= sched_deadline <= sched_period

       In addition, under the current implementation,  all  of	the  parameter
       values must be at least 1024 (i.e., just over one microsecond, which is
       the resolution of the implementation), and less than 2^63.  If  any  of
       these checks fails, sched_setattr(2) fails with the error EINVAL.

       The  CBS	 guarantees  non-interference  between	tasks,	by  throttling
       threads that attempt to over-run their specified Runtime.

       To ensure deadline scheduling guarantees, the kernel must prevent situ-
       ations where the set of SCHED_DEADLINE threads is not feasible (schedu-
       lable) within the given	constraints.   The  kernel  thus  performs  an
       admittance  test	 when  setting	or  changing SCHED_DEADLINE policy and
       attributes.  This admission test calculates whether the change is  fea-
       sible; if it is not, sched_setattr(2) fails with the error EBUSY.

       For  example,  it  is required (but not necessarily sufficient) for the
       total utilization to be less than or equal to the total number of  CPUs
       available,  where,  since each thread can maximally run for Runtime per
       Period, that thread's utilization is its Runtime divided by its Period.

       In order to fulfill the guarantees that	are  made  when	 a  thread  is
       admitted	 to  the SCHED_DEADLINE policy, SCHED_DEADLINE threads are the
       highest priority (user controllable) threads  in	 the  system;  if  any
       SCHED_DEADLINE thread is runnable, it will preempt any thread scheduled
       under one of the other policies.

       A call to fork(2) by a thread scheduled under the SCHED_DEADLINE policy
       will  fail  with	 the error EAGAIN, unless the thread has its reset-on-
       fork flag set (see below).

       A SCHED_DEADLINE thread that calls sched_yield(2) will yield  the  cur-
       rent job and wait for a new period to begin.

   SCHED_OTHER: Default Linux time-sharing scheduling
       SCHED_OTHER  can be used at only static priority 0 (i.e., threads under
       real-time policies always have priority	over  SCHED_OTHER  processes).
       SCHED_OTHER  is	the  standard  Linux  time-sharing  scheduler  that is
       intended for all threads that do	 not  require  the  special  real-time

       The  thread to run is chosen from the static priority 0 list based on a
       dynamic priority that is determined only inside this list.  The dynamic
       priority	 is  based  on the nice value (see below) and is increased for
       each time quantum the thread is ready to run, but denied to run by  the
       scheduler.  This ensures fair progress among all SCHED_OTHER threads.

   The nice value
       The  nice  value	 is an attribute that can be used to influence the CPU
       scheduler to favor or disfavor a process in scheduling  decisions.   It
       affects	the scheduling of SCHED_OTHER and SCHED_BATCH (see below) pro-
       cesses.	The nice value can be modified using nice(2),  setpriority(2),
       or sched_setattr(2).

       According  to  POSIX.1, the nice value is a per-process attribute; that
       is, the threads in a process should share a nice	 value.	  However,  on
       Linux,  the  nice value is a per-thread attribute: different threads in
       the same process may have different nice values.

       The range of the nice value varies  across  UNIX	 systems.   On	modern
       Linux, the range is -20 (high priority) to +19 (low priority).  On some
       other systems, the range is -20..20.  Very early Linux kernels  (Before
       Linux 2.0) had the range -infinity..15.

       The  degree  to which the nice value affects the relative scheduling of
       SCHED_OTHER processes likewise varies across UNIX  systems  and	across
       Linux kernel versions.

       With the advent of the CFS scheduler in kernel 2.6.23, Linux adopted an
       algorithm that causes relative differences in nice  values  to  have  a
       much stronger effect.  In the current implementation, each unit of dif-
       ference in the nice values of two processes results in a factor of 1.25
       in  the	degree	to  which  the	scheduler  favors  the higher priority
       process.	 This causes very low nice values (+19) to truly provide  lit-
       tle  CPU	 to a process whenever there is any other higher priority load
       on the system, and makes high nice values (-20) deliver most of the CPU
       to applications that require it (e.g., some audio applications).

       On  Linux, the RLIMIT_NICE resource limit can be used to define a limit
       to which an unprivileged process's nice value can be raised; see	 setr-
       limit(2) for details.

       For further details on the nice value, see the subsections on the auto-
       group feature and group scheduling, below.

   SCHED_BATCH: Scheduling batch processes
       (Since Linux 2.6.16.)  SCHED_BATCH can be used only at static  priority
       0.   This  policy  is  similar  to SCHED_OTHER in that it schedules the
       thread according to its dynamic priority (based	on  the	 nice  value).
       The  difference	is that this policy will cause the scheduler to always
       assume that the thread is CPU-intensive.	 Consequently,	the  scheduler
       will  apply a small scheduling penalty with respect to wakeup behavior,
       so that this thread is mildly disfavored in scheduling decisions.

       This policy is useful for workloads that are noninteractive, but do not
       want to lower their nice value, and for workloads that want a determin-
       istic scheduling policy without interactivity causing extra preemptions
       (between the workload's tasks).

   SCHED_IDLE: Scheduling very low priority jobs
       (Since  Linux  2.6.23.)	SCHED_IDLE can be used only at static priority
       0; the process nice value has no influence for this policy.

       This policy is intended for running  jobs  at  extremely	 low  priority
       (lower  even  than a +19 nice value with the SCHED_OTHER or SCHED_BATCH

   Resetting scheduling policy for child processes
       Each thread has a reset-on-fork scheduling flag.	  When	this  flag  is
       set,  children  created by fork(2) do not inherit privileged scheduling
       policies.  The reset-on-fork flag can be set by either:

       *  ORing the SCHED_RESET_ON_FORK flag into  the	policy	argument  when
	  calling sched_setscheduler(2) (since Linux 2.6.32); or

       *  specifying  the  SCHED_FLAG_RESET_ON_FORK  flag  in attr.sched_flags
	  when calling sched_setattr(2).

       Note that the constants used with these two APIs have different	names.
       The  state of the reset-on-fork flag can analogously be retrieved using
       sched_getscheduler(2) and sched_getattr(2).

       The reset-on-fork feature is intended for media-playback	 applications,
       and  can	 be  used  to  prevent	applications evading the RLIMIT_RTTIME
       resource limit (see getrlimit(2)) by creating multiple child processes.

       More precisely, if the reset-on-fork flag is set, the  following	 rules
       apply for subsequently created children:

       *  If  the  calling  thread  has	 a  scheduling policy of SCHED_FIFO or
	  SCHED_RR, the policy is reset to SCHED_OTHER in child processes.

       *  If the calling process has a negative nice value, the nice value  is
	  reset to zero in child processes.

       After  the reset-on-fork flag has been enabled, it can be reset only if
       the thread has the CAP_SYS_NICE capability.  This flag is  disabled  in
       child processes created by fork(2).

   Privileges and resource limits
       In  Linux kernels before 2.6.12, only privileged (CAP_SYS_NICE) threads
       can set a nonzero static priority (i.e.,	 set  a	 real-time  scheduling
       policy).	  The  only  change that an unprivileged thread can make is to
       set the SCHED_OTHER policy, and this can be done only if the  effective
       user ID of the caller matches the real or effective user ID of the tar-
       get thread (i.e., the thread specified by pid) whose  policy  is	 being

       A  thread must be privileged (CAP_SYS_NICE) in order to set or modify a
       SCHED_DEADLINE policy.

       Since Linux 2.6.12, the RLIMIT_RTPRIO resource limit defines a  ceiling
       on  an  unprivileged  thread's  static  priority	 for  the SCHED_RR and
       SCHED_FIFO policies.  The rules for changing scheduling policy and pri-
       ority are as follows:

       *  If  an  unprivileged	thread has a nonzero RLIMIT_RTPRIO soft limit,
	  then it can change its scheduling policy and	priority,  subject  to
	  the  restriction  that  the priority cannot be set to a value higher
	  than the maximum of its current priority and its RLIMIT_RTPRIO  soft

       *  If  the  RLIMIT_RTPRIO  soft	limit  is  0,  then the only permitted
	  changes are to lower the priority, or to switch to  a	 non-real-time

       *  Subject to the same rules, another unprivileged thread can also make
	  these changes, as long as the effective user ID of the thread making
	  the  change  matches	the  real  or  effective user ID of the target

       *  Special rules apply for the SCHED_IDLE  policy.   In	Linux  kernels
	  before  2.6.39,  an  unprivileged thread operating under this policy
	  cannot  change  its  policy,	regardless  of	the   value   of   its
	  RLIMIT_RTPRIO	 resource  limit.   In	Linux kernels since 2.6.39, an
	  unprivileged thread can switch to  either  the  SCHED_BATCH  or  the
	  SCHED_OTHER  policy so long as its nice value falls within the range
	  permitted by its RLIMIT_NICE resource limit (see getrlimit(2)).

       Privileged (CAP_SYS_NICE) threads ignore the  RLIMIT_RTPRIO  limit;  as
       with  older kernels, they can make arbitrary changes to scheduling pol-
       icy  and	 priority.   See  getrlimit(2)	for  further  information   on

   Limiting the CPU usage of real-time and deadline processes
       A nonblocking infinite loop in a thread scheduled under the SCHED_FIFO,
       SCHED_RR, or SCHED_DEADLINE policy  can	potentially  block  all	 other
       threads	from  accessing	 the  CPU forever.  Prior to Linux 2.6.25, the
       only way of preventing a runaway real-time process  from	 freezing  the
       system  was  to	run  (at the console) a shell scheduled under a higher
       static priority than the tested application.  This allows an  emergency
       kill of tested real-time applications that do not block or terminate as

       Since Linux 2.6.25, there are other techniques for dealing with runaway
       real-time  and  deadline	 processes.   One  of  these  is  to  use  the
       RLIMIT_RTTIME resource limit to set a ceiling on the CPU	 time  that  a
       real-time process may consume.  See getrlimit(2) for details.

       Since  version  2.6.25, Linux also provides two /proc files that can be
       used to reserve a certain amount of CPU time to be  used	 by  non-real-
       time  processes.	  Reserving  CPU  time in this fashion allows some CPU
       time to be allocated to (say) a root shell that can be used to  kill  a
       runaway	process.  Both of these files specify time values in microsec-

	      This file specifies a scheduling period that  is	equivalent  to
	      100%  CPU bandwidth.  The value in this file can range from 1 to
	      INT_MAX, giving an operating range of 1 microsecond to around 35
	      minutes.	 The  default  value in this file is 1,000,000 (1 sec-

	      The value in this file specifies how much of the	"period"  time
	      can be used by all real-time and deadline scheduled processes on
	      the system.  The value  in  this	file  can  range  from	-1  to
	      INT_MAX-1.   Specifying  -1  makes  the  runtime the same as the
	      period; that is, no CPU time is set aside for non-real-time pro-
	      cesses (which was the Linux behavior before kernel 2.6.25).  The
	      default value in this file is 950,000  (0.95  seconds),  meaning
	      that 5% of the CPU time is reserved for processes that don't run
	      under a real-time or deadline scheduling policy.

   Response time
       A blocked high priority thread waiting for I/O has a  certain  response
       time  before  it	 is  scheduled	again.	 The  device driver writer can
       greatly reduce this response time by using a "slow interrupt" interrupt

       Child  processes	 inherit the scheduling policy and parameters across a
       fork(2).	 The scheduling policy and  parameters	are  preserved	across

       Memory  locking is usually needed for real-time processes to avoid pag-
       ing delays; this can be done with mlock(2) or mlockall(2).

   The autogroup feature
       Since Linux 2.6.38, the kernel provides a feature known as autogrouping
       to improve interactive desktop performance in the face of multiprocess,
       CPU-intensive workloads such as building the Linux  kernel  with	 large
       numbers of parallel build processes (i.e., the make(1) -j flag).

       This  feature  operates	in  conjunction	 with  the  CFS	 scheduler and
       requires a kernel that is configured with CONFIG_SCHED_AUTOGROUP.  On a
       running	system,	 this  feature	is  enabled  or	 disabled via the file
       /proc/sys/kernel/sched_autogroup_enabled; a value  of  0	 disables  the
       feature, while a value of 1 enables it.	The default value in this file
       is 1, unless the kernel was booted with the noautogroup parameter.

       A new autogroup is created when a new session is created via setsid(2);
       this  happens,  for  example, when a new terminal window is started.  A
       new process created by fork(2) inherits its parent's autogroup  member-
       ship.   Thus, all of the processes in a session are members of the same
       autogroup.  An autogroup	 is  automatically  destroyed  when  the  last
       process in the group terminates.

       When  autogrouping  is  enabled, all of the members of an autogroup are
       placed in the same kernel scheduler "task group".   The	CFS  scheduler
       employs	an  algorithm  that  equalizes	the distribution of CPU cycles
       across task groups.  The benefits of this for interactive desktop  per-
       formance can be described via the following example.

       Suppose that there are two autogroups competing for the same CPU (i.e.,
       presume either a single CPU system or the use of taskset(1) to  confine
       all  the	 processes to the same CPU on an SMP system).  The first group
       contains ten CPU-bound processes	 from  a  kernel  build	 started  with
       make -j10.   The	 other	contains  a  single CPU-bound process: a video
       player.	The effect of autogrouping is that the two  groups  will  each
       receive half of the CPU cycles.	That is, the video player will receive
       50% of the CPU cycles, rather than just 9% of the cycles,  which	 would
       likely lead to degraded video playback.	The situation on an SMP system
       is more complex, but the general effect is the same: the scheduler dis-
       tributes CPU cycles across task groups such that an autogroup that con-
       tains a large number of CPU-bound processes does not end up hogging CPU
       cycles at the expense of the other jobs on the system.

       A  process's  autogroup	(task  group) membership can be viewed via the
       file /proc/[pid]/autogroup:

	   $ cat /proc/1/autogroup
	   /autogroup-1 nice 0

       This file can also be used to modify the CPU bandwidth allocated to  an
       autogroup.  This is done by writing a number in the "nice" range to the
       file to set the autogroup's nice value.	The allowed range is from  +19
       (low priority) to -20 (high priority).  (Writing values outside of this
       range causes write(2) to fail with the error EINVAL.)

       The autogroup nice setting has the same meaning	as  the	 process  nice
       value,  but applies to distribution of CPU cycles to the autogroup as a
       whole, based on the relative nice values of other  autogroups.	For  a
       process	inside an autogroup, the CPU cycles that it receives will be a
       product of the autogroup's nice value (compared	to  other  autogroups)
       and  the	 process's nice value (compared to other processes in the same

       The use of the cgroups(7) CPU controller to place processes in  cgroups
       other than the root CPU cgroup overrides the effect of autogrouping.

       The  autogroup  feature groups only processes scheduled under non-real-
       time policies (SCHED_OTHER, SCHED_BATCH, and SCHED_IDLE).  It does  not
       group processes scheduled under real-time and deadline policies.	 Those
       processes are scheduled according to the rules described earlier.

   The nice value and group scheduling
       When scheduling non-real-time processes (i.e.,  those  scheduled	 under
       the  SCHED_OTHER, SCHED_BATCH, and SCHED_IDLE policies), the CFS sched-
       uler employs a technique known as "group scheduling", if the kernel was
       configured with the CONFIG_FAIR_GROUP_SCHED option (which is typical).

       Under  group  scheduling, threads are scheduled in "task groups".  Task
       groups have a hierarchical relationship, rooted under the initial  task
       group  on  the system, known as the "root task group".  Task groups are
       formed in the following circumstances:

       *  All of the threads in a CPU cgroup form a task group.	 The parent of
	  this	task  group  is	 the  task  group  of the corresponding parent

       *  If autogrouping is  enabled,	then  all  of  the  threads  that  are
	  (implicitly) placed in an autogroup (i.e., the same session, as cre-
	  ated by setsid(2)) form a task group.	 Each new autogroup is thus  a
	  separate  task group.	 The root task group is the parent of all such

       *  If autogrouping is enabled, then the root task group consists of all
	  processes  in the root CPU cgroup that were not otherwise implicitly
	  placed into a new autogroup.

       *  If autogrouping is disabled, then the root task  group  consists  of
	  all processes in the root CPU cgroup.

       *  If  group  scheduling	 was disabled (i.e., the kernel was configured
	  without CONFIG_FAIR_GROUP_SCHED), then all of the processes  on  the
	  system are notionally placed in a single task group.

       Under  group scheduling, a thread's nice value has an effect for sched-
       uling decisions only relative to other threads in the same task	group.
       This  has  some	surprising  consequences  in  terms of the traditional
       semantics of the nice value on UNIX systems.  In particular,  if	 auto-
       grouping	 is  enabled  (which is the default in various distributions),
       then employing setpriority(2) or nice(1) on a  process  has  an	effect
       only  for  scheduling  relative to other processes executed in the same
       session (typically: the same terminal window).

       Conversely, for two processes that are (for example) the sole CPU-bound
       processes in different sessions (e.g., different terminal windows, each
       of whose jobs are tied to different  autogroups),  modifying  the  nice
       value  of  the process in one of the sessions has no effect in terms of
       the scheduler's decisions relative to the process in the other session.
       A  possibly useful workaround here is to use a command such as the fol-
       lowing to modify the autogroup nice value for all of the processes in a
       terminal session:

	   $ echo 10 > /proc/self/autogroup

   Real-time features in the mainline Linux kernel
       Since  kernel version 2.6.18, Linux is gradually becoming equipped with
       real-time capabilities, most of which are derived from the former real-
       time-preempt  patch set.	 Until the patches have been completely merged
       into the mainline kernel, they must be installed to  achieve  the  best
       real-time performance.  These patches are named:


       and  can	 be  downloaded	 from  <http://www.kernel.org/pub/linux/kernel

       Without the patches and prior to their full inclusion into the mainline
       kernel,	the  kernel  configuration  offers  only  the three preemption
       EMPT_DESKTOP  which  respectively  provide  no,	some, and considerable
       reduction of the worst-case scheduling latency.

       With the patches applied or after their full inclusion into  the	 main-
       line   kernel,  the  additional	configuration  item  CONFIG_PREEMPT_RT
       becomes available.  If this is selected, Linux is  transformed  into  a
       regular	real-time  operating system.  The FIFO and RR scheduling poli-
       cies are then used to run a thread with true real-time priority	and  a
       minimum worst-case scheduling latency.

       The  cgroups(7) CPU controller can be used to limit the CPU consumption
       of groups of processes.

       Originally, Standard Linux was intended as a general-purpose  operating
       system  being able to handle background processes, interactive applica-
       tions, and less demanding  real-time  applications  (applications  that
       need  to usually meet timing deadlines).	 Although the Linux kernel 2.6
       allowed for kernel preemption and the newly introduced  O(1)  scheduler
       ensures	that  the  time	 needed to schedule is fixed and deterministic
       irrespective of the number of active tasks,  true  real-time  computing
       was not possible up to kernel version 2.6.17.

       chrt(1), taskset(1), getpriority(2), mlock(2), mlockall(2), munlock(2),
       munlockall(2), nice(2), sched_get_priority_max(2),
       sched_get_priority_min(2), sched_getaffinity(2), sched_getparam(2),
       sched_getscheduler(2), sched_rr_get_interval(2), sched_setaffinity(2),
       sched_setparam(2), sched_setscheduler(2), sched_yield(2),
       setpriority(2), pthread_getaffinity_np(3), pthread_setaffinity_np(3),
       sched_getcpu(3), capabilities(7), cpuset(7)

       Programming  for	 the  real  world  -  POSIX.4  by Bill O. Gallmeister,
       O'Reilly & Associates, Inc., ISBN 1-56592-074-0.

       The   Linux   kernel   source   files	Documentation/scheduler/sched-
       deadline.txt,		   Documentation/scheduler/sched-rt-group.txt,
       Documentation/scheduler/sched-design-CFS.txt,			   and

       This  page  is  part of release 4.10 of the Linux man-pages project.  A
       description of the project, information about reporting bugs,  and  the
       latest	  version     of     this    page,    can    be	   found    at

Linux				  2016-10-08			      SCHED(7)