I was wondering how the Hot Add and SCA features affect the performance of small VM (2 vCPU in my case).
Enabling the Hot Add feature disables vNUMA feature that starts working when the number of virtual CPUs is greater than 8 and "can improve performance by facilitating guest operating system and application NUMA optimizations".
According to a good article "CPU Hot Add Performance in vSphere 6.7" this may reduce performance by 2 - 8%.
But does it affect VMs with a small number of vCPU? Let's check.
To mitigate “L1 Terminal Fault” vulnerabilities on Intel processors (CVE-2018-3646) VMware released KB55806. They propose two options:
- ESXi Side-Channel-Aware Scheduler (SCAv1) for ESXi 5.5, 6.0, 6.5, and 6.7 prior to 6.7u2.
- ESXi Side-Channel-Aware Scheduler v2 (SCAv2) for ESXi 6.7u2 (13006603) and later.
SCAv1 disables Hyper Threading, but SCAv2 does not. But all of them should affect performance, even though VMware says "Retain up to 100% performance for low to moderate loaded systems".
