Open Stack

Hello/
After chasing links and your examples, I found this example is good for
beginners like me, I want to show that for previous people.

https://access.redhat.com/documentation/en-us/red_hat_openstack_platform/16.2/html-single/configuring_the_compute_service_for_instance_creation/index#proc_configuring-compute-nodes-for-cpu-pinning_cpu-pinning

Thank you much.

Nguyen Huu Khoi


On Thu, Mar 23, 2023 at 9:54 PM Sean Mooney <smooney at redhat.com> wrote:

> On Thu, 2023-03-23 at 14:51 +0100, Dmitriy Rabotyagov 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.
> yep exactly.
> without geting into all the details the host reserved cpu option was added
> in the really early days and then vcpu_pin_set was
> added to adress the fact that the existing option didnt really work the
> way peopel wanted.
> it was later used for cpu pinning and we realise we wanted to have 2
> sepreate pools of cpus
>
> cpu_shared_set for shared core useed by floating vms (anything with out
> hw:cpu_policy=dedicated) and
> cpu_dedicated_set for explictlly pinned vms.
>
> in general using cpu_shared_set and cpu_dedicated_set is a much more
> intitive way to resver cores since you get to select exaction which
> cores can be used for nova vms.
>
> that allows you do the use systemd or other tools like taskset  to
> affiites nova-cpu or libvirtd or  sshd to run  on core that wont have vms
> that prevents the vms form staving those host process of cpu resouces.
> >
> > 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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