View source for CPU shielding using /proc and /dev/cpuset

== Interrupt shielding ==

In order to shield CPUs from individual interrupts being serviced on them you have to make sure that the following kernel configuration parameter is set:

*CONFIG_IRQBALANCE

Then make sure that the interrupts are not automatically balanced by the irqbalance daemon. This daemon is started from the irqbalance init script. To disable once do:

{{cmdroot|/etc/init.d/irqbalance stop}}

To disable after next reboot do:

{{cmdroot|chkconfig irqbalance off}}

After this you can change the CPU affinity mask of each interrupt by doing:

{{cmdroot|echo ''hex_mask'' > /proc/irq/''irq_number''/smp_affinity}}

To check that the affinity mask has been set you can check the contents of the smp_affinity file. {{NOTE|The mask is updated the next time an interrupt is serviced. So you may not see the change immediately.}}

More information can be found in {{path|/usr/src/kernel/Documentation/IRQ-affinity.txt}}.

== Process shielding ==

The kernel has an cpuset feature that allows you to create cpusets for real-time purposes. The kernel interface is proc filesystem based. It is described in {{path|/usr/src/kernel/Documentation/cpusets.txt}}.

Here is a quick example of how to use cpuset to reserve one cpu for your real-time process on a 4 cpu machine:

{{cmdroot|mkdir /dev/cpuset/rt0}}

{{cmdroot|echo 0 > /dev/cpuset/rt0/cpus}}

{{cmdroot|echo 0 > /dev/cpuset/rt0/mems}}

{{cmdroot|echo 1 > /dev/cpuset/rt0/cpu_exclusive}}

{{cmdroot|echo $RT_PROC_PID > /dev/cpuset/rt0/tasks}}

{{cmdroot|mkdir /dev/cpuset/system}}

{{cmdroot|echo 1-3 > /dev/cpuset/system/cpus}}

{{cmdroot|echo 0 > /dev/cpuset/system/mems}}

{{cmdroot|echo 1 > /dev/cpuset/system/cpu_exclusive}}

{{cmdroot|for pid in $(cat /dev/cpuset/tasks); do /bin/echo $pid > /dev/cpuset/system/tasks; done}}