Open Stack

On Mon, 2023-09-04 at 12:59 +0200, Karera Tony wrote:
> Hello Danny,
> 
> I am actually using Broadwell-noTSX-IBRS on all the servers but I have seen
> that some flags are not there in the older servers.
> 
> The flags below to be specific.
> 
> hwp hwp_act_window hwp_pkg_req
so hwp is apprentlly intels pstate contol
based on https://unix.stackexchange.com/a/43540

i dont belive this is normally exposed to a guest but
if you are seeign differnce between hosts then that likely
means you have disabled pstates also know as "intel speedstep" on 
some of the host and not others.

> 
> Regards
> 
> Tony Karera
> 
> 
> 
> 
> On Fri, Sep 1, 2023 at 4:05 PM <smooney at redhat.com> wrote:
> 
> > On Fri, 2023-09-01 at 14:56 +0200, Karera Tony wrote:
> > > Hello Danny,
> > > 
> > > Thanks for the feedback.
> > > 
> > > use a lowest common denominator cpu_model : Does this mean changing the
> > > servers ?
> > 
> > it means tha tif you have a mix of cpus in the deployment you shoudl
> > hardcod
> > to the older of the diffent cpu models i.e skylake or whatever it may be
> > in your case.
> > 
> > 
> > https://docs.openstack.org/nova/latest/configuration/config.html#libvirt.cpu_models
> > 
> > [libvirt]
> > cpu_mode=custom
> > cpu_models=skylake
> > 
> > in more recent release we replaced the older cpu_model with cpu_models
> > with is a comma sperated
> > list of models in prefernce order. i.e. nova will use the first cpu_modle
> > in the list that work
> > on the current host. not that while this give extra flexiblity it vs just
> > using the oldest cpu model
> > it does limit the set of hosts you can migrate too but means you can have
> > better perfromance so its
> > a tradeoff. performance vs portablity.
> > 
> > the error you mentioned can also be caused by micorocode updates.
> > intel remove TSX and MPX i beilve in the last 2 years form come of there
> > cpus
> > that breaks live migration if a vm was create with access to that cpu
> > instruction
> > 
> > the only way to resolve that is to cold migrate the guest.
> > i.e. if a vm is currently booted with cpu_model X it cannot be modifed
> > while the guest is running
> > so you either need to update the config option and reboot all the vms or
> > more particlaly update the config
> > and then cold migrate them which will allow you to move the instnace(your
> > orginal goal) while allowing
> > the new cpu model to take effect.
> > 
> > novas default for the cpu model when not set is with our default cpu_mode
> > is host_model
> > meaning whatever model best matches the current hosts cpu.
> > 
> > that is the correct default in general but if you have mixed cpu
> > generatiosn in your cloud its not ideal.
> > 
> > hopefuly that helps
> > 
> > > 
> > > Regards
> > > 
> > > Tony Karera
> > > 
> > > 
> > > 
> > > 
> > > On Fri, Sep 1, 2023 at 12:37 PM Danny Webb <Danny.Webb at thehutgroup.com>
> > > wrote:
> > > 
> > > > It means that you have CPUs with incompatible flags or you've got
> > > > differing kernel versions that expose different flags or you've got
> > > > differing libvirt versions that expose different flags.  You either
> > need to
> > > > use a lowest common denominator cpu_model or do a cold migration.
> > > > ------------------------------
> > > > *From:* Karera Tony <tonykarera at gmail.com>
> > > > *Sent:* 01 September 2023 10:13
> > > > *To:* openstack-discuss <openstack-discuss at lists.openstack.org>
> > > > *Subject:* Live migration error
> > > > 
> > > > 
> > > > * CAUTION: This email originates from outside THG *
> > > > ------------------------------
> > > > Hello Team,
> > > > 
> > > > I am trying to migrate instances from one host to another but I am
> > getting
> > > > this error.
> > > > 
> > > > *Error: *Failed to live migrate instance to host "compute1". Details
> > > > <http://10.10.13.31/admin/instances/#message_details>
> > > > Migration pre-check error: Unacceptable CPU info: CPU doesn't have
> > > > compatibility. 0 Refer to
> > > > http://libvirt.org/html/libvirt-libvirt-host.html#virCPUCompareResult
> > > > (HTTP 400) (Request-ID: req-9dfdfe2e-70fa-481a-bd3d-c2c76a6e93da)
> > > > 
> > > > Any idea on how to fix this?
> > > > 
> > > > Regards
> > > > 
> > > > Tony Karera
> > > > 
> > > > 
> > > > 
> > 
> >