Open Stack

Just to double check with you, given that you have
cpu_overcommit_ratio>1, 2 sockets and HT enabled, and each CPU has 32
physical cores, then it should be defined like:

[compute]
cpu_shared_set="2-32,34-64,66-96,98-128"?

> 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

чт, 23 мар. 2023 г. в 13:12, Sean Mooney <smooney at redhat.com>:
>
> 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
>
>