How to pin Citrix Hypervisor Virtual CPUs to specific Physical CPUs
Article ID: CTX246466
Updated On:
Description
Citrix Hypervisor maps vCPUs to pCPUs by default in a semi-even way to distribute VM load on the host. In some cases it may be needed to have a specific mapping, for example, if some VMs will be CPU intensive while other wont, the intensive VMs can be mapped to exclusive physical CPUs while the others share resources. This can lead to performance improvements in the Hypervisor.
The following example will be used to change hard affinity. This means where the vCPU is allowed to run. In this sense, once a vCPU is pinned to a pCPU with hard affinity, the vCPU won't be able to run in any other pCPU.
Soft affinity is used to define where does the vCPU prefers to run but it doesn't restrict where it is allowed to run.
To determine which type of mapping to use, analyze the type of workload that the guest VMs are going to be running. Ultimately the best way to determine the best mapping is through testing different configurations with real workloads and observing the results. There is not a perfect ratio since workloads change depending on many factors, such as OS type, patches, apps run by users, employee work schedules, etc.
Instructions
Command definitions
xl vcpu-pin <domain#> <vcpu#> <pCPUhard> <pCPUsoft> (VMs are called domains in Xen terminology)
xl vcpu-list (helps you find the current domain numbers, current pinning and affinity)
Sample commands
xl vcpu-pin 1 2 3 (Pin Domain 1 machine vCPU 2 to pCPU 3 with hard affinity)
xl vcpu-pin 0 1 all 0-2 (Pin domain 0 vCPU 1 with hard affinity to all and soft affinity to 0, 1 and 2 pCPUs)
Sample configuration change, before and after.
[root@lab ~]# xl vcpu-list
Name ID VCPU CPU State Time(s) Affinity (Hard / Soft)
Domain-0 0 0 5 -b- 123489.6 all / all
Domain-0 0 1 10 -b- 123852.0 all / all
Domain-0 0 2 7 -b- 120716.0 all / all
Domain-0 0 3 7 -b- 123082.4 all / all
Domain-0 0 4 10 -b- 120731.4 all / all
Domain-0 0 5 3 -b- 128169.0 all / all
Domain-0 0 6 8 r-- 288875.7 all / all
Domain-0 0 7 10 -b- 134935.5 all / all
Domain-0 0 8 9 -b- 129905.5 all / all
Domain-0 0 9 1 -b- 129339.3 all / all
Domain-0 0 10 11 -b- 131645.5 all / all
Domain-0 0 11 3 -b- 200675.1 all / all
vm1 109 0 1 -b- 13003.2 all / all
vm1 109 1 5 -b- 14843.0 all / all
vm2 122 0 10 -b- 9517.5 all / all
vm2 122 1 6 -b- 2338.2 all / all
vm3 127 0 11 -b- 30649.4 all / all
vm3 127 1 6 -b- 3141.9 all / all
vm4 161 0 1 -b- 21896.7 all / all
vm4 161 1 0 -b- 8084.3 all / all
vm5 237 0 8 -b- 2594.5 all / all
vm6 238 0 5 -b- 4820.9 all / all
vm6 238 1 5 -b- 4608.6 all / all
vm7 242 0 6 -b- 25274.0 all / all
vm7 242 1 4 r-- 468972.1 all / all
vm8 244 0 7 -b- 3969.3 all / all
vm8 244 1 5 -b- 531.4 all / all
vm8 244 2 9 -b- 1251.7 all / all
vm8 244 3 10 -b- 483.6 all / all
vm9 255 0 10 -b- 6186.4 all / all
vm9 255 1 3 -b- 1432.1 all / all
vm10 260 0 11 -b- 4724.3 all / all
vm10 260 1 7 -b- 1342.8 all / all
vm11 262 0 0 -b- 10335.3 all / all
vm11 262 1 9 -b- 5015.9 all / all
xl vcpu-pin 0 0 0
xl vcpu-pin 0 1 1
xl vcpu-pin 0 2 2
xl vcpu-pin 0 3 3
xl vcpu-pin 0 4 4
xl vcpu-pin 0 5 5
xl vcpu-pin 0 6 0
xl vcpu-pin 0 7 1
xl vcpu-pin 0 8 2
xl vcpu-pin 0 9 3
xl vcpu-pin 0 10 4
xl vcpu-pin 0 11 5
xl vcpu-pin 109 0 0
xl vcpu-pin 109 1 1
xl vcpu-pin 122 0 2
xl vcpu-pin 122 1 3
xl vcpu-pin 127 0 4
xl vcpu-pin 127 1 5
xl vcpu-pin 161 0 6
xl vcpu-pin 161 1 7
xl vcpu-pin 237 0 8
xl vcpu-pin 238 0 9
xl vcpu-pin 238 1 10
xl vcpu-pin 242 0 11
xl vcpu-pin 242 1 0
xl vcpu-pin 244 0 1
xl vcpu-pin 244 1 2
xl vcpu-pin 244 2 3
xl vcpu-pin 244 3 4
xl vcpu-pin 255 0 5
xl vcpu-pin 255 1 6
xl vcpu-pin 260 0 7
xl vcpu-pin 260 1 8
xl vcpu-pin 262 0 9
xl vcpu-pin 262 1 10
[root@lab ~]# xl vcpu-list
Name ID VCPU CPU State Time(s) Affinity (Hard / Soft)
Domain-0 0 0 0 -b- 123501.4 0 / all
Domain-0 0 1 1 -b- 123861.7 1 / all
Domain-0 0 2 2 -b- 120728.9 2 / all
Domain-0 0 3 3 -b- 123093.3 3 / all
Domain-0 0 4 4 -b- 120743.4 4 / all
Domain-0 0 5 5 -b- 128180.6 5 / all
Domain-0 0 6 0 -b- 288889.3 0 / all
Domain-0 0 7 1 -b- 134947.2 1 / all
Domain-0 0 8 2 -b- 129918.8 2 / all
Domain-0 0 9 3 r-- 129355.4 3 / all
Domain-0 0 10 4 -b- 131656.6 4 / all
Domain-0 0 11 5 -b- 200695.5 5 / all
vm1 109 0 0 -b- 13008.5 0 / all
vm1 109 1 1 -b- 14848.2 1 / all
vm2 122 0 2 -b- 9523.1 2 / all
vm2 122 1 3 -b- 2339.5 3 / all
vm3 127 0 4 -b- 30668.0 4 / all
vm3 127 1 5 -b- 3143.6 5 / all
vm4 161 0 6 -b- 21921.4 6 / all
vm4 161 1 7 -b- 8099.3 7 / all
vm5 237 0 8 -b- 2596.5 8 / all
vm6 238 0 9 -b- 4827.6 9 / all
vm6 238 1 10 -b- 4614.7 10 / all
vm7 242 0 11 -b- 25316.6 11 / all
vm7 242 1 0 r-- 469803.4 0 / all
vm8 244 0 1 -b- 3979.5 1 / all
vm8 244 1 2 -b- 532.7 2 / all
vm8 244 2 3 -b- 1254.8 3 / all
vm8 244 3 4 -b- 484.7 4 / all
vm9 255 0 5 -b- 6207.9 5 / all
vm9 255 1 6 -b- 1438.0 6 / all
vm10 260 0 7 -b- 4735.4 7 / all
vm10 260 1 8 -b- 1346.1 8 / all
vm11 262 0 9 -b- 10400.3 9 / all
vm11 262 1 10 -b- 5044.6 10 / all
