On Fri, 2 Feb 2018 16:51:23 +0100 Viktor Mihajlovski <mihajlov@xxxxxxxxxxxxxxxxxx> wrote: > On 02.02.2018 16:22, Luiz Capitulino wrote: > > On Fri, 2 Feb 2018 16:08:25 +0100 > > Viktor Mihajlovski <mihajlov@xxxxxxxxxxxxxxxxxx> wrote: > > > >>>> A disabled guest CPU is represented as halted in the QEMU object model > >>>> and can therefore be identified by the QMP query-cpus command. > >>>> > >>>> The initial patch proposal to expose this via virsh vcpuinfo was not > >>>> considered to be desirable because there was a concern that legacy > >>>> management software might be confused seeing halted vcpus. Therefore the > >>>> state information was added to the cpu domain statistics. > >>>> > >>>> One issue we're facing is that the semantics of "halted" are different > >>>> between s390 and at least x86. The question might be whether they are > >>>> different enough to grant a specific "disabled" indicator. > >>> > >>> From your description, it looks like they are completely > >>> different. On x86, a CPU that is online and in use can be moved > >>> between halted and non-halted state many times a second. > >>> > >>> If that's the case, we can probably fix this without breaking > >>> existing code: explicitly documenting the semantics of > >>> "vcpu.<n>.halted" at virConnectGetAllDomainStats() to mean "not > >>> online" (i.e. the s390 semantics, not the x86 one), and making > >>> qemuMonitorGetCpuHalted() s390-specific. > >>> > >>> Possibly a better long-term solution is to deprecate > >>> "vcpu.<n>.halted" and make "vcpu.<n>.state" work correctly on > >>> s390> > >> As it seems that nobody was ever *really* interested in x86.halted, one > >> could also return 0 unconditionally there (and for other > >> expensive-to-query arches)? > > > > The most important question I have is: does this solution satisfy the > > needs of upper management? That is, if we implement the solution suggested > > by Eduardo than the feature of automatically hotplugging more CPUs > > will only work for s390. Is this OK? > > > > If yes, then I think this is the best solution. And the next question > > would be: Viktor, can you change this in libvirt while we fix query-cpus > > in QEMU? > > > The latest proposal was to use a flag for query-cpus (like full-state) > which would control the set of properties queried and reported. If this > is the way we decide to go, I can make the necessary changes in libvirt. OK, I thought we were going to do both. Because, if libvirt only wants the halted field for s390 then why issue query-cpus at all in other archs? > > Btw, I guess OpenStack ran into this issue just because this field > > slipped into domstats API and ceilometer issues that command... > > > >>> It would be also interesting to update QEMU QMP documentation to > >>> clarify the arch-specific semantics of "halted". > >>> > >> > >> > > > >
