On Fri, 16 Feb 2018 17:08:36 +0100 Viktor Mihajlovski <mihaj...@linux.vnet.ibm.com> wrote:
> v5 synopsis: Split out HMP changes from Patch 2 into Patch 5. Please > re-review, as I've removed the a-b/r-b from Patch 2 > as well. > > This series consolidates patches around a performance issue > caused by the usage of QMP query-cpus. > > A performance issue was found in an OpenStack environment, where > ceilometer was collecting domain statistics with libvirt. The domain > statistics reported by libvirt include the vCPU halted state, which > in turn is retrieved with QMP query-cpus. > > This causes two issues: > 1. Performance: on most architectures query-cpus needs to issue a KVM ioctl > to find out whether a vCPU was halted. This is not the case for s390 > but query-cpus is always causing the vCPU to exit the VM. > > 2. Semantics: on x86 and other architectures, halted is a highly transient > state, which is likely to have already changed shortly after the state > information has been retrieved. This is not the case for s390, where > halted is an indication that the vCPU is stopped, meaning its not > available to the guest operating system until it has been restarted. Thanks, queued to s390-next.
