b9f88dc071
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>
97 lines
3.2 KiB
Python
97 lines
3.2 KiB
Python
# -*- Mode: Python -*-
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# vim: filetype=python
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##
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# = Introduction
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#
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# This document describes all commands currently supported by QMP.
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#
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# Most of the time their usage is exactly the same as in the user Monitor, this
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# means that any other document which also describe commands (the manpage,
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# QEMU's manual, etc) can and should be consulted.
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#
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# QMP has two types of commands: regular and query commands. Regular commands
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# usually change the Virtual Machine's state someway, while query commands just
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# return information. The sections below are divided accordingly.
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#
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# It's important to observe that all communication examples are formatted in
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# a reader-friendly way, so that they're easier to understand. However, in real
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# protocol usage, they're emitted as a single line.
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#
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# Also, the following notation is used to denote data flow:
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#
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# Example:
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#
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# ::
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#
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# -> data issued by the Client
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# <- Server data response
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#
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# Please, refer to the QMP specification (docs/interop/qmp-spec.txt) for
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# detailed information on the Server command and response formats.
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#
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# = Stability Considerations
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#
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# The current QMP command set (described in this file) may be useful for a
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# number of use cases, however it's limited and several commands have bad
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# defined semantics, specially with regard to command completion.
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#
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# These problems are going to be solved incrementally in the next QEMU releases
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# and we're going to establish a deprecation policy for badly defined commands.
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#
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# If you're planning to adopt QMP, please observe the following:
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#
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# 1. The deprecation policy will take effect and be documented soon, please
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# check the documentation of each used command as soon as a new release of
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# QEMU is available
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#
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# 2. DO NOT rely on anything which is not explicit documented
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#
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# 3. Errors, in special, are not documented. Applications should NOT check
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# for specific errors classes or data (it's strongly recommended to only
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# check for the "error" key)
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#
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##
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{ 'include': 'pragma.json' }
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# Documentation generated with qapi-gen.py is in source order, with
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# included sub-schemas inserted at the first include directive
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# (subsequent include directives have no effect). To get a sane and
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# stable order, it's best to include each sub-schema just once, or
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# include it first right here.
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{ 'include': 'error.json' }
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{ 'include': 'common.json' }
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{ 'include': 'sockets.json' }
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{ 'include': 'run-state.json' }
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{ 'include': 'crypto.json' }
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{ 'include': 'block.json' }
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{ 'include': 'block-export.json' }
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{ 'include': 'char.json' }
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{ 'include': 'dump.json' }
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{ 'include': 'job.json' }
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{ 'include': 'net.json' }
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{ 'include': 'rdma.json' }
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{ 'include': 'rocker.json' }
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{ 'include': 'tpm.json' }
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{ 'include': 'ui.json' }
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{ 'include': 'authz.json' }
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{ 'include': 'migration.json' }
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{ 'include': 'transaction.json' }
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{ 'include': 'trace.json' }
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{ 'include': 'compat.json' }
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{ 'include': 'control.json' }
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{ 'include': 'introspect.json' }
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{ 'include': 'qom.json' }
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{ 'include': 'qdev.json' }
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{ 'include': 'machine.json' }
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{ 'include': 'machine-target.json' }
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{ 'include': 'replay.json' }
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{ 'include': 'yank.json' }
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{ 'include': 'misc.json' }
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{ 'include': 'misc-target.json' }
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{ 'include': 'audio.json' }
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{ 'include': 'acpi.json' }
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{ 'include': 'pci.json' }
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{ 'include': 'stats.json' }
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