From cf7405bc0228c795557e19bacbaa3b145bb17370 Mon Sep 17 00:00:00 2001
From: Paolo Bonzini <pbonzini@redhat.com>
Date: Tue, 24 May 2022 19:13:16 +0200
Subject: qmp: add filtering of statistics by name

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>
---
 qapi/stats.json | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

(limited to 'qapi/stats.json')

diff --git a/qapi/stats.json b/qapi/stats.json
index 503918e..2f8bfe8 100644
--- a/qapi/stats.json
+++ b/qapi/stats.json
@@ -75,11 +75,14 @@
 # Indicates a set of statistics that should be returned by query-stats.
 #
 # @provider: provider for which to return statistics.
+
+# @names: statistics to be returned (all if omitted).
 #
 # Since: 7.1
 ##
 { 'struct': 'StatsRequest',
-  'data': { 'provider': 'StatsProvider' } }
+  'data': { 'provider': 'StatsProvider',
+            '*names': [ 'str' ] } }
 
 ##
 # @StatsVCPUFilter:
@@ -99,6 +102,7 @@
 # that target:
 # - which vCPUs to request statistics for
 # - which providers to request statistics from
+# - which named values to return within each provider
 #
 # Since: 7.1
 ##
-- 
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