[linuxkernelnewbies] CPU shielding using /proc and /dev/cpuset - RTwiki

[Peter Teoh]

http://rt.wiki.kernel.org/index.php/CPU_shielding_using_/proc_and_/dev/cpuset CPU shielding using /proc and /dev/cpuset From RTwiki Jump to: navigation, search 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: # /etc/init.d/irqbalance stop To disable after next reboot do: # chkconfig irqbalance off After this you can change the CPU affinity mask of each interrupt by doing: # 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 /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 /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: # mkdir /dev/cpuset/rt0 # echo 0 > /dev/cpuset/rt0/cpus # echo 0 > /dev/cpuset/rt0/mems # echo 1 > /dev/cpuset/rt0/cpu_exclusive # echo $RT_PROC_PID > /dev/cpuset/rt0/tasks # mkdir /dev/cpuset/system # echo 1-3 > /dev/cpuset/system/cpus # echo 0 > /dev/cpuset/system/mems # echo 1 > /dev/cpuset/system/cpu_exclusive # for pid in $(cat /dev/cpuset/tasks); do /bin/echo $pid > /dev/cpuset/system/tasks; done