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authorFrancesco Romani <fromani@redhat.com>2015-01-12 14:11:13 +0100
committerKevin Wolf <kwolf@redhat.com>2015-02-06 17:24:21 +0100
commite2462113b2003085ad16f15e1442ded64e2d9a29 (patch)
tree113c7d9301d441e8a63bcf75b578f6201f1d6751 /qapi
parent6440d44cea84451ee9facb1237a4e7251631df80 (diff)
block: add event when disk usage exceeds threshold
Managing applications, like oVirt (http://www.ovirt.org), make extensive use of thin-provisioned disk images. To let the guest run smoothly and be not unnecessarily paused, oVirt sets a disk usage threshold (so called 'high water mark') based on the occupation of the device, and automatically extends the image once the threshold is reached or exceeded. In order to detect the crossing of the threshold, oVirt has no choice but aggressively polling the QEMU monitor using the query-blockstats command. This lead to unnecessary system load, and is made even worse under scale: deployments with hundreds of VMs are no longer rare. To fix this, this patch adds: * A new monitor command `block-set-write-threshold', to set a mark for a given block device. * A new event `BLOCK_WRITE_THRESHOLD', to report if a block device usage exceeds the threshold. * A new `write_threshold' field into the `BlockDeviceInfo' structure, to report the configured threshold. This will allow the managing application to use smarter and more efficient monitoring, greatly reducing the need of polling. [Updated qemu-iotests 067 output to add the new 'write_threshold' property. --Stefan] [Changed g_assert_false() to !g_assert() to fix the build on older glib versions. --Kevin] Signed-off-by: Francesco Romani <fromani@redhat.com> Reviewed-by: Eric Blake <eblake@redhat.com> Message-id: 1421068273-692-1-git-send-email-fromani@redhat.com Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Diffstat (limited to 'qapi')
-rw-r--r--qapi/block-core.json51
1 files changed, 50 insertions, 1 deletions
diff --git a/qapi/block-core.json b/qapi/block-core.json
index b7d9772444..a3fdaf02ba 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -257,6 +257,9 @@
#
# @cache: the cache mode used for the block device (since: 2.3)
#
+# @write_threshold: configured write threshold for the device.
+# 0 if disabled. (Since 2.3)
+#
# Since: 0.14.0
#
##
@@ -271,7 +274,8 @@
'*bps_max': 'int', '*bps_rd_max': 'int',
'*bps_wr_max': 'int', '*iops_max': 'int',
'*iops_rd_max': 'int', '*iops_wr_max': 'int',
- '*iops_size': 'int', 'cache': 'BlockdevCacheInfo' } }
+ '*iops_size': 'int', 'cache': 'BlockdevCacheInfo',
+ 'write_threshold': 'int' } }
##
# @BlockDeviceIoStatus:
@@ -1917,3 +1921,48 @@
##
{ 'enum': 'PreallocMode',
'data': [ 'off', 'metadata', 'falloc', 'full' ] }
+
+##
+# @BLOCK_WRITE_THRESHOLD
+#
+# Emitted when writes on block device reaches or exceeds the
+# configured write threshold. For thin-provisioned devices, this
+# means the device should be extended to avoid pausing for
+# disk exhaustion.
+# The event is one shot. Once triggered, it needs to be
+# re-registered with another block-set-threshold command.
+#
+# @node-name: graph node name on which the threshold was exceeded.
+#
+# @amount-exceeded: amount of data which exceeded the threshold, in bytes.
+#
+# @write-threshold: last configured threshold, in bytes.
+#
+# Since: 2.3
+##
+{ 'event': 'BLOCK_WRITE_THRESHOLD',
+ 'data': { 'node-name': 'str',
+ 'amount-exceeded': 'uint64',
+ 'write-threshold': 'uint64' } }
+
+##
+# @block-set-write-threshold
+#
+# Change the write threshold for a block drive. An event will be delivered
+# if a write to this block drive crosses the configured threshold.
+# This is useful to transparently resize thin-provisioned drives without
+# the guest OS noticing.
+#
+# @node-name: graph node name on which the threshold must be set.
+#
+# @write-threshold: configured threshold for the block device, bytes.
+# Use 0 to disable the threshold.
+#
+# Returns: Nothing on success
+# If @node name is not found on the block device graph,
+# DeviceNotFound
+#
+# Since: 2.3
+##
+{ 'command': 'block-set-write-threshold',
+ 'data': { 'node-name': 'str', 'write-threshold': 'uint64' } }