CPU affinity?
CPU affinity is nothing but a scheduler property that "bonds" a
process to a given set of CPUs on the SMP 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. For example,
application such as Oracle (ERP apps) use # of cpus per instance
licensed. You can bound Oracle to specific CPU to avoid license
problem. This is a really useful on large server having 4 or 8 CPUS
Setting processor affinity for a certain task or process using taskset
command
taskset 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. However taskset is not installed by default. You need to
install schedutils (Linux scheduler utilities) package.
Install schedutils
Debian Linux:
# apt-get install schedutils
Red Hat Enterprise Linux:
# up2date schedutils
OR
# rpm -ivh schedutils*
Under latest version of Debian / Ubuntu Linux taskset is installed by
default using util-linux package.
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. For example:
* 0x00000001 is processor #0 (1st processor)
* 0x00000003 is processors #0 and #1
* 0x00000004 is processors #2 (3rd processor)
To set the processor affinity of process 13545 to processor #0 (1st
processor) type following command:
# taskset 0x00000001 -p 13545
If you find a bitmask hard to use, then you can specify a numerical
list of processors instead of a bitmask using -c flag:
# taskset -c 1 -p 13545
# taskset -c 3,4 -p 13545
Where,
* -p : Operate on an existing PID and not launch a new task
(default is to launch a new task)
