Re: [libvirt] [RFC] kvm: x86: export vCPU halted state to sysfs

>> 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)?

> It would be also interesting to update QEMU QMP documentation to > clarify the arch-specific semantics of "halted". >