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27 From: Luiz Capitulino <lcapitulino@redhat.com>
28 To: <qemu-devel@nongnu.org>
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31 Subject: [PATCH 3/3] docs: document virtio-balloon stats
32 Date: Fri, 14 Dec 2012 13:49:42 -0200
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52 Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
53 ---
54 docs/virtio-balloon-stats.txt | 91 +++++++++++++++++++++++++++++++++++++++++++
55 1 file changed, 91 insertions(+)
56 create mode 100644 docs/virtio-balloon-stats.txt
58 diff --git a/docs/virtio-balloon-stats.txt b/docs/virtio-balloon-stats.txt
59 new file mode 100644
60 index 0000000..990e746
61 --- /dev/null
62 +++ b/docs/virtio-balloon-stats.txt
63 @@ -0,0 +1,91 @@
64 +virtio balloon memory statistics
65 +================================
66 +
67 +The virtio balloon driver supports guest memory statistics reporting. These
68 +statistics are available to QEMU users as QOM (QEMU Object Model) device
69 +properties via a polling mechanism.
70 +
71 +Basically, clients first have to enable polling, then they can query the
72 +available statistics.
73 +
74 +There are two control properties and six memory statistics properties.
75 +
76 +The control properties are:
77 +
78 + o stats-polling-interval: polling time interval in seconds, it can be:
79 +
80 + > 0 enables polling in the specified interval. If polling is already
81 + enabled, the polling time interval will be changed to the new value
82 +
83 + 0 disables polling. Previous polled statistics are still valid and
84 + can be queried.
85 +
86 + o stats-last-update: last stats update timestamp, in seconds
87 +
88 +The following statistics are available, all values are in bytes:
89 +
90 + o stat-swap-in
91 + o stat-swap-out
92 + o stat-major-faults
93 + o stat-minor-faults
94 + o stat-free-memory
95 + o stat-total-memory
96 +
97 +Also, please note the following:
98 +
99 + - If a statistic is queried before the timer is enabled or if the guest
100 + doesn't support a particular statistic, an error will be returned
101 +
102 + - Previously polled statistics remain available even if the timer is
103 + later disabled
104 +
105 + - Polling can be enabled even if the guest doesn't support memory
106 + statistics or its balloon driver hasn't been loaded. Applications
107 + can check this condition by checking that stats-last-update doesn't
108 + change
109 +
110 + - The polling timer is only re-armed when the guest responds to the
111 + statistics request. This means that if a (buggy) guest doesn't
112 + ever respond to the request the timer will never be re-armed,
113 + which has the same effect as disabling polling
114 +
115 +Here are a few examples. The virtio-balloon device is assumed to be in the
116 +'/machine/peripheral-anon/device[1]' QOM path.
117 +
118 +Enable polling with 2 seconds interval:
119 +
120 +{ "execute": "qom-set",
121 + "arguments": { "path": "/machine/peripheral-anon/device[1]",
122 + "property": "stats-polling-interval", "value": 2 } }
123 +
124 +{ "return": {} }
125 +
126 +Change polling to 10 seconds:
127 +
128 +{ "execute": "qom-set",
129 + "arguments": { "path": "/machine/peripheral-anon/device[1]",
130 + "property": "stats-polling-interval", "value": 10 } }
131 +
132 +{ "return": {} }
133 +
134 +Get last update timestamp and free memory stat:
135 +
136 +{ "execute": "qom-get",
137 + "arguments": { "path": "/machine/peripheral-anon/device[1]",
138 + "property": "stats-last-update" } }
139 +
140 +{ "return": 1354629634 }
141 +
142 +{ "execute": "qom-get",
143 + "arguments": { "path": "/machine/peripheral-anon/device[1]",
144 + "property": "stat-free-memory" } }
145 +
146 +{ "return": 845115392 }
147 +
148 +Disable polling:
149 +
150 +{ "execute": "qom-set",
151 + "arguments": { "path": "/machine/peripheral-anon/device[1]",
152 + "property": "stats-polling-interval", "value": 0 } }
153 +
154 +{ "return": {} }
155 --
156 1.8.0