Open Stack

Hi.
Too many new things for me. It is interesting. I will read more. Thank
you Dmitriy
Rabotyagov
Nice to meet you!

Nguyen Huu Khoi


On Thu, Mar 23, 2023 at 8:58 PM Dmitriy Rabotyagov <noonedeadpunk at gmail.com>
wrote:

> Just in case, you DO have options to control cpu and ram reservation
> for the hypervisor. It's just more about that, that it's not the best
> way to do it, especially if you're overcommitting, as things in real
> life are more complicated then just defining the amount of reserved
> CPUs.
>
> For example, if you have cpu_allocation_ratio set to 3, then you're
> getting 3 times more CPUs to signup VMs then you actually have
> (cores*sockets*threads*cpu_allocation_ratio). With that you really
> can't set any decent amount of reserved CPUs that will 100% ensure
> that hypervisor will be able to gain required resources at any given
> time. So with that approach the only option is to disable cpu
> overcommit, but even then you might get CPU in socket 1 fully utilized
> which might have negative side-effects for the hypervisor.
>
> And based on that, as Sean has mentioned, you can tell nova to
> explicitly exclude specific cores from being utilized, which will make
> them reserved for the hypervisor.
>
> чт, 23 мар. 2023 г. в 14:35, Nguyễn Hữu Khôi <nguyenhuukhoinw at gmail.com>:
> >
> > Ok. I will try to understand it. I will let you know when I get it.
> > Many thanks for your help. :)
> >
> > On Thu, Mar 23, 2023, 8:14 PM Dmitriy Rabotyagov <
> noonedeadpunk at gmail.com> wrote:
> >>
> >> 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
> >> >
> >> >
>
>
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