On Mon, 12 Feb 2018 13:14:29 +0100 Viktor Mihajlovski <mihaj...@linux.vnet.ibm.com> wrote:
> This series consolidates patches around a performance issue > caused by the usage of QMP query-cpus. Thank you for consolidating this; it was a bit hard to follow the different discussions. > > 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. > > The following patches help to alleviate the issues: > > Patch 1/3: > Adds architecture specific data to the QMP CpuInfo type, exposing > the existing s390 cpu-state in QMP. The cpu-state is a representation > more adequate than the ambiguous 'halted' condition. > > Changes since original v2: > - fixed cpu-state usage in hw/intc/s390_flic.c, necessary because > master was updated in the meantime > - removed superfluous newline while printing cpu-state So this is adding s390x info in query-cpus (presumably for legacy callers?)... > > Patch 2/3: > Adds a new QMP function query-cpus-fast, which will only retrieve > vCPU information that can be obtained without interrupting the > vCPUs of a running VM. It introduces a new return type CpuInfoFast > with the subset of fields meeting this condition. Specifically, the > halted state is not part of CpuInfoFast. QMP clients like libvirt > are encouraged to switch to the new API for vCPU information. > > Changes since original v2: > - dropped optional halted state from CpuInfoFast ...this is adding the new query-cpus-fast... > > Patch 3/3: > Adds the s390-specific cpu state to CpuInfoFast, allowing management > apps to find out whether a vCPU is in the stopped state. This extension > leads to a partial duplication of field definitions from CpuInfo > to CpuInfoFast. This should be tolerable if CpuInfo is deprecated and > eventually removed. ...and this is adding the s390x state to query-cpus-fast, right? > > Luiz Capitulino (1): > qmp: add query-cpus-fast > > Viktor Mihajlovski (2): > qmp: expose s390-specific CPU info > qmp: add architecture specific cpu data for query-cpus-fast > > cpus.c | 54 ++++++++++++++++++++ > hmp-commands-info.hx | 14 ++++++ > hmp.c | 33 +++++++++++++ > hmp.h | 1 + > hw/intc/s390_flic.c | 4 +- > hw/s390x/s390-virtio-ccw.c | 2 +- > qapi-schema.json | 121 > ++++++++++++++++++++++++++++++++++++++++++++- > target/s390x/cpu.c | 24 ++++----- > target/s390x/cpu.h | 7 +-- > target/s390x/kvm.c | 8 +-- > target/s390x/sigp.c | 38 +++++++------- > 11 files changed, 262 insertions(+), 44 deletions(-) >