[Qemu-devel] [PATCH 3/3] docs: document virtio-balloon stats

[Luiz Capitulino <lcapitulino@redhat.com>]

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
---
 docs/virtio-balloon-stats.txt | 87 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 87 insertions(+)
 create mode 100644 docs/virtio-balloon-stats.txt

diff --git a/docs/virtio-balloon-stats.txt b/docs/virtio-balloon-stats.txt
new file mode 100644
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+virtio balloon memory statistics
+================================
+
+The virtio balloon driver supports guest memory statistics reporting. These
+statistics are available to QEMU users as QOM (QEMU Object Model) device
+properties via a polling mechanism.
+
+Basically, clients first have to enable polling, then they can query the
+available statistics.
+
+There are two control properties and six memory statistics properties.
+
+The control properties are:
+
+ o stats-polling-interval: polling time interval in seconds, it can be:
+
+   > 0  enables polling in the specified interval. If polling is already
+        enabled, the polling time interval will be changed to the new value
+
+   0    disables polling. Previous polled statistics are still valid and
+        can be queried.
+
+ o stats-last-update: last stats update timestamp, in seconds
+
+The following statistics are available, all values are in bytes:
+
+ o stat-swap-in
+ o stat-swap-out
+ o stat-major-faults
+ o stat-minor-faults
+ o stat-free-memory
+ o stat-total-memory
+
+Also, please note the following:
+
+ - If a statistic is queried before the timer is enabled or if the guest
+   doesn't support a particular statistic, an error will be returned
+
+ - Previously polled statistics remain available even if the timer is
+   later disabled
+
+ - The polling timer is only re-armed when the guest answers to the
+   statistics request. This means that if the guest takes too long to
+   respond (say, a few seconds) this delay will end up being added to the
+   poll interval. Also, if a (buggy) guest doesn't ever respond, the
+   statistics won't get updated and the timer disarmed
+
+Here are a few examples. The virtio-balloon device is assumed to be in the
+'/machine/peripheral-anon/device[1]' QOM path.
+
+Enable polling with 2 seconds interval:
+
+{ "execute": "qom-set",
+             "arguments": { "path": "/machine/peripheral-anon/device[1]",
+			 "property": "stats-polling-interval", "value": 2 } }
+
+{ "return": {} }
+
+Change polling to 10 seconds:
+
+{ "execute": "qom-set",
+             "arguments": { "path": "/machine/peripheral-anon/device[1]",
+			 "property": "stats-polling-interval", "value": 10 } }
+
+{ "return": {} }
+
+Get last update timestamp and free memory stat:
+
+{ "execute": "qom-get",
+  "arguments": { "path": "/machine/peripheral-anon/device[1]",
+  "property": "stats-last-update" } }
+
+{ "return": 1354629634 }
+
+{ "execute": "qom-get",
+  "arguments": { "path": "/machine/peripheral-anon/device[1]",
+  "property": "stat-free-memory" } }
+
+{ "return": 845115392 }
+
+Disable polling:
+
+{ "execute": "qom-set",
+             "arguments": { "path": "/machine/peripheral-anon/device[1]",
+			 "property": "stats-polling-interval", "value": 0 } }
+
+{ "return": {} }
-- 
1.8.0