realtime:documentation:howto:tools:cpu_shielding
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realtime:documentation:howto:tools:cpu_shielding [2017/05/08 23:51] srodrig1 |
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| - | ====== CPU shielding using /proc and /dev/cpuset ====== | + | |
| - | ===== Interrupt shielding ===== | + | |
| - | ==== Kernel Space ==== | + | |
| - | 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 | + | |
| - | ==== User Space ==== | + | |
| - | 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: | + | |
| - | <code bash> | + | |
| - | $ /etc/init.d/irqbalance stop | + | |
| - | </code> | + | |
| - | To disable after next reboot do: | + | |
| - | <code bash> | + | |
| - | $ chkconfig irqbalance off | + | |
| - | </code> | + | |
| - | After this you can change the CPU affinity mask of each interrupt by doing: | + | |
| - | <code bash> | + | |
| - | $ echo hex_mask > /proc/irq/<irq_number>/smp_affinity | + | |
| - | </code> | + | |
| - | To check that the affinity mask has been set you can check the contents of the smp_affinity file. | + | |
| - | <WRAP center round info 100%> | + | |
| - | The mask is updated the next time an interrupt is serviced. So you may not see the change immediately. | + | |
| - | </WRAP> | + | |
| - | More information can be found in [[https://www.kernel.org/doc/Documentation/IRQ-affinity.txt|IRQ affinity]] | + | |
| - | ===== 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 [[https://www.kernel.org/doc/Documentation/cgroup-v1/cpusets.txt|cpusets]]. | + | |
| - | Each cpuset is represented by a directory in the cgroup file system containing (on top of the standard cgroup files) the following files describing that cpuset: | + | |
| - | <WRAP center round box 100%> | + | |
| - | * cpus: list of CPUs in that cpuset | + | |
| - | * mems: list of Memory Nodes in that cpuset | + | |
| - | * memory_migrate flag: if set, move pages to cpusets nodes | + | |
| - | * cpu_exclusive flag: is cpu placement exclusive? | + | |
| - | * mem_exclusive flag: is memory placement exclusive? | + | |
| - | * mem_hardwall flag: is memory allocation hardwalled | + | |
| - | * memory_pressure: measure of how much paging pressure in cpuset | + | |
| - | * memory_spread_page flag: if set, spread page cache evenly on allowed nodes | + | |
| - | * memory_spread_slab flag: if set, spread slab cache evenly on allowed nodes | + | |
| - | * sched_load_balance flag: if set, load balance within CPUs on that cpuset | + | |
| - | * sched_relax_domain_level: the searching range when migrating tasks | + | |
| - | </WRAP> | + | |
| - | In addition, the root cpuset only has the following file: | + | |
| - | <WRAP center round box 100%> | + | |
| - | * memory_pressure_enabled flag: compute memory_pressure? | + | |
| - | </WRAP> | + | |
| - | Here is a quick example of how to use cpuset to reserve one cpu for your real-time process on a 4 cpu machine: | + | |
| - | <code bash> | + | |
| - | $ 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 | + | |
| - | </code> | + | |
realtime/documentation/howto/tools/cpu_shielding.1494287472.txt.gz · Last modified: 2017/05/08 23:51 by srodrig1
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