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. Series looks good to me. I'd be happy to take it through the s390 tree with some a-bs/r-bs for patches 2 and 5, but have given some r-bs as well in case someone else wants to take it. > > 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: > > Patch 1/5: > 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. > > Patch 2/5: > 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. > > Patch 3/5: > 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. > > Patch 4/5: > Starts the deprecation of query-cpus. > > Patch 5/5 (NEW): > Changes HMP 'info cpus' to use query-cpus-fast. Was part of 2/5 > initially. > > Series v4 -> v5: > Overall: Updated r-b's and moved HMP changes into a seperate patch. > > Patch 1/5: > o Updated commit message to clarify why no HMP change > > Patch 2/5: > o Split out HMP changes > o Removed r-b cohuck, a-b eblake > > Series v3 -> v4: > Overall: Instead of adding a new HMP 'info cpus_fast', changed > 'info cpus' to use query-cpus-fast directly. > > Patch 1/4: > o Don't report s390-specific data in HMP 'info cpus' > > Patch 2/4: > o Change HMP 'info cpus' to use query-cpus-fast and > to return only basic information (no arch-specific data) > o Drop HMP 'info cpus_fast' > o Fixed typo in commit message > > Patch 3/4: > o Drop HMP-related changes > > Patch 4/4: > o Drop HMP-related changes > > Series v2 -> v3: > Overall: Added r-b's and a-b's. > > Patch 2/4: > o Fixed commit message with respect to the halted field > disposition. > o Fixed grammar in qapi-schema documentation. > > Patch 3/4: > o Use CpuInfoS390 type for both query-cpus and query-cpus-fast per > Eric Blake's comment. > o Dropped 'duplication blurb' from commit message as it doesn't > provide relevant information other than query-cpus should be > deprecated, which is done in the next patch now. > > Series v1 -> v2: > Patch 2/3: > 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. > > Patch 3/3: > 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 (4): > qmp: expose s390-specific CPU info > qmp: add architecture specific cpu data for query-cpus-fast > qemu-doc: deprecate query-cpus > hmp: change hmp_info_cpus to use query-cpus-fast > > cpus.c | 54 +++++++++++++++++++++ > hmp.c | 41 +++------------- > hw/intc/s390_flic.c | 4 +- > hw/s390x/s390-virtio-ccw.c | 2 +- > monitor.c | 13 +++-- > qapi-schema.json | 115 > ++++++++++++++++++++++++++++++++++++++++++++- > qemu-doc.texi | 4 ++ > target/s390x/cpu.c | 24 +++++----- > target/s390x/cpu.h | 7 +-- > target/s390x/kvm.c | 8 ++-- > target/s390x/sigp.c | 38 +++++++-------- > 11 files changed, 228 insertions(+), 82 deletions(-) >
