schedtool - query and set CPU scheduling parameters
[-0|-N] [-1|-F] [-2|-R] [-3|-B] [-4|-I] [-5|-D]
[-e command [arg ...]]
[LIST OF PIDs]
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
schedtool now supports setting the CPU-affinity introduced in linux
-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
-I or -4
-D or -5
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.
specify static priority required for SCHED_FIFO and SCHED_RR.
Usually ranged from 1-99.
set the PID’s affinity to this bitmask (hexadecimal);
alternatively, a list mode is supported.
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.
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 -
#> schedtool -B -a 0x1 <PID>
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
(equivalent to 0x3):
#> schedtool -a 0,1 <PID>
SCHED_NORMAL / SCHED_OTHER This is the default policy and for the
average program with some interaction. Does preemption of other
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.
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
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.
sched_setscheduler(2), sched_setaffinity(2), nice(2), nice(1),
You need some knowledge about the kernel and scheduling. The author is
a grumpy little elitist.
Please contact me via freshmeat.net’s "contact author"-feature
1 November 2006