CPU shielding using /proc and /dev/cpuset

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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}}.
 
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}}.
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Here is a quick example of how to use cpuset to reserve one cpu for your real-time process on a 4 cpu machine:
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{{cmdroot|mkdir /dev/cpuset/rt0}}
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{{cmdroot|echo 0 > /dev/cpuset/rt0/cpus}}
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{{cmdroot|echo 0 > /dev/cpuset/rt0/mems}}
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{{cmdroot|echo 1 > /dev/cpuset/rt0/cpu_exclusive}}
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{{cmdroot|echo $RT_PROC_PID > /dev/cpuset/rt0/tasks}}
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{{cmdroot|mkdir /dev/cpuset/system}}
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{{cmdroot|echo 1-3 > /dev/cpuset/system/cpus}}
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{{cmdroot|echo 0 > /dev/cpuset/system/mems}}
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{{cmdroot|echo 1 > /dev/cpuset/system/cpu_exclusive}}
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{{cmdroot|for pid in $(cat /dev/cpuset/tasks); do /bin/echo $pid > /dev/cpuset/system/tasks; done}}

Revision as of 13:34, 14 June 2007

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

Retrieved from "https://rt.wiki.kernel.org/index.php?title=CPU_shielding_using_/proc_and_/dev/cpuset&oldid=1710"
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