The next version of Linux will introduce boolean statistics, which
can only have 0 or 1 values. Support them in the schema and in
the HMP command.
Suggested-by: Amneesh Singh <natto@weirdnatto.in>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Allow retrieving only a subset of statistics. This can be useful
for example in order to plot a subset of the statistics many times
a second: KVM publishes ~40 statistics for each vCPU on x86; retrieving
and serializing all of them would be useless.
Another use will be in HMP in the following patch; implementing the
filter in the backend is easy enough that it was deemed okay to make
this a public interface.
Example:
{ "execute": "query-stats",
"arguments": {
"target": "vcpu",
"vcpus": [ "/machine/unattached/device[2]",
"/machine/unattached/device[4]" ],
"providers": [
{ "provider": "kvm",
"names": [ "l1d_flush", "exits" ] } } }
{ "return": {
"vcpus": [
{ "path": "/machine/unattached/device[2]"
"providers": [
{ "provider": "kvm",
"stats": [ { "name": "l1d_flush", "value": 41213 },
{ "name": "exits", "value": 74291 } ] } ] },
{ "path": "/machine/unattached/device[4]"
"providers": [
{ "provider": "kvm",
"stats": [ { "name": "l1d_flush", "value": 16132 },
{ "name": "exits", "value": 57922 } ] } ] } ] } }
Extracted from a patch by Mark Kanda.
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Allow retrieving the statistics from a specific provider only.
This can be used in the future by HMP commands such as "info
sync-profile" or "info profile". The next patch also adds
filter-by-provider capabilities to the HMP equivalent of
query-stats, "info stats".
Example:
{ "execute": "query-stats",
"arguments": {
"target": "vm",
"providers": [
{ "provider": "kvm" } ] } }
The QAPI is a bit more verbose than just a list of StatsProvider,
so that it can be subsequently extended with filtering of statistics
by name.
If a provider is specified more than once in the filter, each request
will be included separately in the output.
Extracted from a patch by Mark Kanda.
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Introduce a simple filtering of statistics, that allows to retrieve
statistics for a subset of the guest vCPUs. This will be used for
example by the HMP monitor, in order to retrieve the statistics
for the currently selected CPU.
Example:
{ "execute": "query-stats",
"arguments": {
"target": "vcpu",
"vcpus": [ "/machine/unattached/device[2]",
"/machine/unattached/device[4]" ] } }
Extracted from a patch by Mark Kanda.
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Add support for querying fd-based KVM stats - as introduced by Linux kernel
commit:
cb082bfab59a ("KVM: stats: Add fd-based API to read binary stats data")
This allows the user to analyze the behavior of the VM without access
to debugfs.
Signed-off-by: Mark Kanda <mark.kanda@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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>
