https://kb.vmware.com/s/article/2002181
https://kb.vmware.com/s/article/2001003
http://www.joshodgers.com/2013/01/05/how-much-cpu-ready-is-ok/
http://www.vmcalc.com/
vCPU to Core Ratio - The number of VM vCPUs allocated compared to the number of physical CPU cores available.
If workloads are CPU-intensive, the vCPU-to-core ratio will need to be smaller; if workloads are not CPU-intensive, the vCPU-to-core ratio can be larger. A typical vCPU-to-core ratio for server workloads is about 4:1—four vCPUs allocated for each available physical core. However, this can be much higher if workloads are not CPU-intensive.
%READY - the percentage of time that the virtual machine was ready but could not be scheduled to run on a physical CPU.Note: The result of above calculations are a sum of each virtual CPUs %RDY time. Individual core Ready time can be roughly estimated by dividing by the number of cores. However, it is more accurate to go by the vCPU metrics themselves. vCPU metrics are only collected in realtime by default.
Performance Threshold:
10% per vCPU based on the following guide:
Good: 1% to 5%
Moderate: 6% to 9%
Bad: 10%+
If the load average is too high, and the ready time is not caused by CPU limiting, adjust the CPU load on the host.
To adjust the CPU load on the host, either:
1) Increase the number of physical CPUs on the host
2) Decrease the number of virtual CPUs allocated to the host. To decrease the number of virtual CPUs allocated to the host, either:
- Reduce the total number of CPUs allocated to all of the virtual machines running on the ESX host. For more information, see Determining if multiple virtual CPUs are causing performance issues (1005362).
- Reduce the number of virtual machines running on the host.
For Production server workloads
<2.5% CPU Ready Generally No Problem!
2.5%-5% CPU Ready Minimal contention that should be monitored during peak times
5%-10% CPU Ready Significant Contention that should be investigated & addressed
>10% CPU Ready Serious Contention to be investigated & addressed ASAP!
However, applications which are latency sensitive may be severely impacted even with low levels of CPU ready, these types of VMs should be on clusters with lower CPU overcommitment, leverage DRS rules to separate the contending workloads or in extreme cases, dedicated clusters.2.5%-5% CPU Ready Minimal contention that should be monitored during peak times
5%-10% CPU Ready Significant Contention that should be investigated & addressed
>10% CPU Ready Serious Contention to be investigated & addressed ASAP!
On the flip side, Some servers are much more tolerant to CPU ready, and 5%-10% CPU ready or higher may not noticeably impact performance.
For Virtual Desktop workloads, what level of CPU ready is acceptable will largely depend on the individual user (ie: Power User verses Task Worker). Keep in mind virtual desktop deployments generally have high CPU consolidation ratios of around 6:1 all the way to >12:1.
I would suggest the following , again as a rule of thumb
<5% CPU Ready Generally No Problem!
5%-10% CPU Ready Minimal contention that should be monitored during peak times
>10% CPU Ready Contention to be investigated & addressed where the end user experience is being impacted.
5%-10% CPU Ready Minimal contention that should be monitored during peak times
>10% CPU Ready Contention to be investigated & addressed where the end user experience is being impacted.
Ready time greater than 10 percent could be a performance concern.
However, some less CPU-sensitive applications and VMs can have much
higher values of ready time and still perform satisfactorily.
EXAMPLE:
HOST Dell R710 CPU Xeon L5520 @ 2.2GHz
CPUs 2 sock x 4 cores
CPU HT enabled yes
vCPUs 16
ESXI 6.0, 4192238
http://www.four2.org/cpubusy/cpubusy.zip
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| HOST CPU Ready |
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| Calculating CPU cycles and contention |
Results:
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| Different configurations |
| HOST | VM1 | VM2 | VM3 | VM4 | ||||||||||||||
| VMs | vCPU on Host |
CPU Stress | VM1 cpubusy-result |
VM1 CPU | VM2 CPU | VM3 CPU | VM4 CPU | CPU usage |
Summation Ready, ms |
CPU ready % |
Summation Ready, ms |
CPU ready % |
Summation Ready, ms |
CPU ready % |
Summation Ready, ms |
CPU ready % |
Summation Ready, ms |
|
| 1 | 16 vCPU | cpubusy | 0.546 | 12 | na | na | na | ~18 | 500 | 0.2 | 600 | na | na | na | na | na | na | |
| 1 | 16 vCPU | cpuz+cpubusy | 0.905 | 100 | na | na | na | ~51 | 1330 | 0.4 | 1400 | na | na | na | na | na | na | |
| 2 | 32 vCPU | cpuz+cpubusy | 0.921 | 100 | 1 | na | na | ~54 | 4800 | 1.2 | 3700 | 5.0 | 1100 | na | na | na | na | |
| 3 | 48 vCPU | cpuz+cpubusy | 0.951 | 100 | 1 | 1 | na | ~55 | 7300 | 1.6 | 5100 | 4.0 | 1260 | 4.0 | 1260 | na | na | |
| 4 | 64 vCPU | cpuz+cpubusy | 0.811 | 100 | 1 | 1 | 1 | 68 | 10700 | 0.6 | 1900 | 0.8 | 2400 | 0.8 | 2415 | 1.5 | 4800 | |
| 4 | 64 vCPU | 2 cpuz+cpubusy | 1.1-1.51 | 100 | 1 | 100 | 1 | 80 | 61900 | 8.2 | 26300 | 0.8 | 2500 | 9.9 | 31800 | 0.8 | 2700 | |
| 4 | 64 vCPU | 4 cpuz+cpubusy | 2.4-3.1 | 100 | 100 | 100 | 100 | 87 | 128000 | 10.5 | 33500 | 10.8 | 34500 | 9.2 | 29500 | 10.0 | 32000 | |
| 4 | 64 vCPU | cpubusy | 0.561 | 8 | 2 | 2 | 2 | 30 | 7100 | 0.9 | 3000 | 0.4 | 1400 | 0.4 | 1400 | 0.5 | 1660 | |
| 6 | 96 vCPU | cpubusy | 0.561-0.577 | 8 | 2 | 2 | 2 | 20 | 13830 | 0.8 | 2700 | 0.7 | 2300 | 0.7 | 2300 | 0.7 | 2300 | |
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| Results in Xorux |