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.
The following patches help to alleviate the issues:
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.
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.
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
Series v1 -> v2:
o Changed formatting of hmp info cpus_fast to match that of
info cpus. This makes it easier for clients to switch to
the fast call.
o Same formatting change for info cpus_fast as in 2/3, only
for s390-specific cpu state.
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 | 28 +++++++++++
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, 257 insertions(+), 44 deletions(-)