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![]() Gathering statistics is important for development, for monitoring and for performance measurement. There are tools such as kvm_stat that do this and they rely on the _user_ knowing the interesting data points rather than the tool (which can treat them as opaque). The commands introduced in this commit introduce QMP support for querying stats; the goal is to take the capabilities of these tools and making them available throughout the whole virtualization stack, so that one can observe, monitor and measure virtual machines without having shell access + root on the host that runs them. query-stats returns a list of all stats per target type (only VM and vCPU to start); future commits add extra options for specifying stat names, vCPU qom paths, and providers. All these are used by the HMP command "info stats". Because of the development usecases around statistics, a good HMP interface is important. query-stats-schemas returns a list of stats included in each target type, with an option for specifying the provider. The concepts in the schema are based on the KVM binary stats' own introspection data, just translated to QAPI. There are two reasons to have a separate schema that is not tied to the QAPI schema. The first is the contents of the schemas: the new introspection data provides different information than the QAPI data, namely unit of measurement, how the numbers are gathered and change (peak/instant/cumulative/histogram), and histogram bucket sizes. There's really no reason to have this kind of metadata in the QAPI introspection schema (except possibly for the unit of measure, but there's a very weak justification). Another reason is the dynamicity of the schema. The QAPI introspection data is very much static; and while QOM is somewhat more dynamic, generally we consider that to be a bug rather than a feature these days. On the other hand, the statistics that are exposed by QEMU might be passed through from another source, such as KVM, and the disadvantages of manually updating the QAPI schema for outweight the benefits from vetting the statistics and filtering out anything that seems "too unstable". Running old QEMU with new kernel is a supported usecase; if old QEMU cannot expose statistics from a new kernel, or if a kernel developer needs to change QEMU before gathering new info from the new kernel, then that is a poor user interface. The framework provides a method to register callbacks for these QMP commands. Most of the work in fact is done by the callbacks, and a large majority of this patch is new QAPI structs and commands. Examples (with KVM stats): - Query all VM stats: { "execute": "query-stats", "arguments" : { "target": "vm" } } { "return": [ { "provider": "kvm", "stats": [ { "name": "max_mmu_page_hash_collisions", "value": 0 }, { "name": "max_mmu_rmap_size", "value": 0 }, { "name": "nx_lpage_splits", "value": 148 }, ... ] }, { "provider": "xyz", "stats": [ ... ] } ] } - Query all vCPU stats: { "execute": "query-stats", "arguments" : { "target": "vcpu" } } { "return": [ { "provider": "kvm", "qom_path": "/machine/unattached/device[0]" "stats": [ { "name": "guest_mode", "value": 0 }, { "name": "directed_yield_successful", "value": 0 }, { "name": "directed_yield_attempted", "value": 106 }, ... ] }, { "provider": "kvm", "qom_path": "/machine/unattached/device[1]" "stats": [ { "name": "guest_mode", "value": 0 }, { "name": "directed_yield_successful", "value": 0 }, { "name": "directed_yield_attempted", "value": 106 }, ... ] }, ] } - Retrieve the schemas: { "execute": "query-stats-schemas" } { "return": [ { "provider": "kvm", "target": "vcpu", "stats": [ { "name": "guest_mode", "unit": "none", "base": 10, "exponent": 0, "type": "instant" }, { "name": "directed_yield_successful", "unit": "none", "base": 10, "exponent": 0, "type": "cumulative" }, ... ] }, { "provider": "kvm", "target": "vm", "stats": [ { "name": "max_mmu_page_hash_collisions", "unit": "none", "base": 10, "exponent": 0, "type": "peak" }, ... ] }, { "provider": "xyz", "target": "vm", "stats": [ ... ] } ] } Signed-off-by: Mark Kanda <mark.kanda@oracle.com> Reviewed-by: Markus Armbruster <armbru@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> |
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hmp-target.h | ||
hmp.h | ||
monitor.h | ||
qdev.h | ||
stats.h |