generally you should not you can use it but the preferd way to do this is use cpu_shared_set and cpu_dedicated_set (in old releases you would have used vcpu_pin_set) https://docs.openstack.org/nova/latest/configuration/config.html#compute.cpu_shared_set https://docs.openstack.org/nova/latest/configuration/config.html#compute.cpu_dedicated_set if you dont need cpu pinning just use cpu_share_set to spcify the cores that can be sued for floatign vms when you use cpu_shared_set and cpu_dedicated_set any cpu not specified are reseved for host use. https://that.guru/blog/cpu-resources/ and https://that.guru/blog/cpu-resources-redux/ have some useful info but that mostly looking at it form a cpu pinning angel althoguh the secon one covers cpu_shared_set, the issue with usein https://docs.openstack.org/nova/latest/configuration/config.html#DEFAULT.reserved_host_cpus is that you have to multiple the number of cores that are resverved by the https://docs.openstack.org/nova/latest/configuration/config.html#DEFAULT.cpu_allocation_ratio which means if you decide to manage that via placement api by using https://docs.openstack.org/nova/latest/configuration/config.html#DEFAULT.initial_cpu_allocation_ratio instead then you need to update your nova.conf to modify the reservationfi you change the allocation ratio. if instead you use cpu_shared_set and cpu_dedicated_set you are specifying exactly which cpus nova can use and the allocation ration nolonger needs to be conisderd. in general you shoudl reserve the first core on each cpu socket for the host os. if you use hyperthreading then both hyperthread of the first cpu core on each socket shoudl be omitted form the cpu_shared_set and cpu_dedicated_set On Thu, 2023-03-23 at 14:44 +0700, Nguyễn Hữu Khôi wrote: > Hello guys. > I am trying google for nova host cpu reserve to prevent host overload but I > cannot find any resource about it. Could you give me some information? > Thanks. > Nguyen Huu Khoi