SCHEDTOOL(8)						      System Manager's Manual						      SCHEDTOOL(8)

NAME

       schedtool - query and set CPU scheduling parameters

SYNOPSIS

       schedtool
	      [-0|-N] [-1|-F] [-2|-R] [-3|-B] [-4|-I] [-5|-D]
	      [-M policy]
	      [-a affinity]
	      [-p prio]
	      [-n nice_level]
	      [-e command [arg ...]]
	      [-r]
	      [-v]
	      [-h]
	      [LIST OF PIDs]

DESCRIPTION

       schedtool can set all CPU scheduling parameters Linux is capable of or display information for given processes.

       Long-running, non-interactive tasks may benefit from SCHED_BATCH as timeslices are longer, less system-time is wasted by computing the next
       runnable process and the caches stay stable.

       Audio/video or other near-realtime applications may run with less skipping if set to SCHED_RR.  Use the static priority-switch -p to desig-
       nate inter-process-hierarchies.

       schedtool now supports setting the CPU-affinity introduced in linux 2.5.8.

OPTIONS

       -N or -0
	      set all PIDs to SCHED_NORMAL/OTHER

       -F or -1
	      to SCHED_FIFO   root-credentials required

       -R or -2
	      to SCHED_RR     root-credentials required

       -B or -3
	      to SCHED_BATCH

       -I or -4
	      to SCHED_ISO

       -D or -5
	      to SCHED_IDLEPRIO

       -M policy
	      for  manual/raw mode; policy is the number of the scheduling policy (see above for 0-4).	This option is mostly for kernel guys that
	      want to test their new implementations.

       -p prio
	      specify static priority required for SCHED_FIFO and SCHED_RR. Usually ranged from 1-99.

       -a affinity
	      set the PID's affinity to this bitmask (hexadecimal); alternatively, a list mode is supported.

       -n nice_level
	      set the PID's nice level; see nice(2), nice(1).

       -e command [arg ...]
	      execute command with given scheduling parameters (overwrites schedtool's process image). See EXAMPLES.

       -r     display min and max priority for each policy.

       -v     be verbose.

       -h     help

EXAMPLES

       To query the $SHELL's policies:

	   #> schedtool $$

       To query some PIDs, namely 1 2 and 3:

	   #> schedtool 1 2 3

       To execute mplayer in SCHED_RR with priority 20. The priority arg is needed for both SCHED_RR and SCHED_FIFO.

	   #> schedtool -R -p 20 -e mplayer -quiet some_file.avi

       To set current shell to SCHED_BATCH, which all programs the shell starts will inherit:

	   #> schedtool -3 $$

       To set all processes with the name 'cpu_hog' to SCHED_BATCH:

	   #> schedtool -3 `pidof cpu_hog`

       To set a process' affinity to only the first CPU (CPU0):

	   #> schedtool -a 0x1 <PID>

       Using the list mode and affinty of CPU0 and CPU3:

	   #> schedtool -a 0,3 <PID>

       A combination of an affinity and a policy-argument is - of course - always possible.

	  #> schedtool -B -a 0x1 <PID>

AFFINITY MASK

       The affinity-argument determines on which CPUs a process is allowed to run. It consists of a simple  bitmask  represented  in  hexadecimal.
       CPU0 is denoted by the least-significant bit, CPU1 by the second least-significant and so on, thus giving:

	   0x1 -> only run on CPU0

	   0x2 -> only run on CPU1

	   0x4 -> only run on CPU2

	   0x8 -> only run on CPU3 ... and so on.

       Multi-target CPUs may be specified using bitwise OR of the values:

	   0x7 -> run on CPUs 0, 1, 2 but NOT on 4

	   0x3 -> run only on CPUs 0 and 1

       The default is to run a process on all CPUs, giving a mask of

	   0xf for all 4 CPUs

	   0xff for all 8 CPUs

AFFINITY MASK - LIST MODE
       Alternatively a list mode is supported where you can specify the CPUs delimited by ",".	The following runs <PID> on CPU0 and CPU1 (equiva-
       lent to 0x3):

	  #> schedtool -a 0,1 <PID>

POLICY OVERVIEW

       SCHED_NORMAL / SCHED_OTHER This is the default policy and for the average program with some interaction.  Does  preemption  of  other  pro-
       cesses.

       SCHED_FIFO First-In, First Out Scheduler, used only for real-time contraints.  Processes in this class are usually not preempted by others,
       they need to free themselves from the CPU via sched_yield() and as such you need special designed  applications.  Use  with  extreme  care.
       ROOT-credentials required.

       SCHED_RR  Round-Robin  Scheduler,  also	used for real-time constraints. CPU-time is assigned in an round-robin fashion with a much smaller
       timeslice than with SCHED_NORMAL and processes in this group are favoured over SCHED_NORMAL. Usable for audio/video applications near  peak
       rate of the system.  ROOT-credentials required.

       SCHED_BATCH  [  since 2.6.16 in mainline ] SCHED_BATCH was designed for non-interactive, CPU-bound applications.  It uses longer timeslices
       (to better exploit the cache), but can be interrupted anytime by other processes in other classes to guaratee interaction  of  the  system.
       Processes in this class are selected last but may result in a considerable speed-up (up to 300%). No interactive boosting is done.

       SCHED_ISO  [  patch  needed ] SCHED_ISO was designed to give users a SCHED_RR-similar class.  To quote Con Kolivas: "This is a non-expiring
       scheduler policy designed to guarantee a timeslice within a reasonable latency while preventing starvation.  Good for gaming, video at  the
       limits of hardware, video capture etc."

       SCHED_IDLEPRIO  [ patch needed ] SCHED_IDLEPRIO is similar to SCHED_BATCH, but was explicitely designed to consume only the time the CPU is
       idle. No interactive boosting is done.  If you used SCHED_BATCH in the -ck kernels this is what you want since 2.6.16

HINTS

       PID 0 means "current process", in our case, schedtool. May occur when using the -e switch.

       Be careful with SCHED_FIFO! You may lock out other processes from the CPU, including your shell.

       For SCHED_BATCH you certainly need the a recent 2.6 kernel.

       A short overview is given in SCHED_DESIGN and the README contains thourough discussion. The INSTALL file also lists all	prerequisites  and
       where you can get patches.

       Affinity 0x0 should never be used.

SEE ALSO

       sched_setscheduler(2), sched_setaffinity(2), nice(2), nice(1), renice(3).

BUGS

       You need some knowledge about the kernel and scheduling. The author is a grumpy little elitist.

AUTHOR

       Freek

       Please contact me via freshmeat.net's "contact author"-feature (http://freshmeat.net/projects/schedtool).

								  1 November 2006						      SCHEDTOOL(8)