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 skip-
ping 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 pol-
icy (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); alterna-
tively, 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 - al-
ways 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-sig-
nificant 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 aver-
age program with some interaction. Does preemption of other processes.
SCHED_FIFO First-In, First Out Scheduler, used only for real-time con-
straints. 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 pro-
cesses in other classes to guaratee interaction of the system. Pro-
cesses 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 explicitly 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 thor-
ough 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)
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