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
> 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
> 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(-)