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libvirt/libvirt-Introduce-support-for-disk-operation-latency-histogram-collection.patch
Jiri Denemark e043cfc857 libvirt-11.10.0-9.el10 
- qemu: capabilities: Probe properties of 'scsi-block' and 'scsi-generic' devices (RHEL-135115)
- qemu: capabilities: Introduce QEMU_CAPS_DEVICE_SCSI_BLOCK_MIGRATE_PR (RHEL-135115)
- RHEL-ONLY: backport test data for 'migrate-pr' capability of 'scsi-block' (RHEL-135115)
- qemu: Implement support for persistent reservation migration control (RHEL-135115)
- qemu: Extract disk setup done via QMP into a separate helper (RHEL-131335)
- qemu: process: Rename 'qemuProcessSetupDiskThrottling' to 'qemuProcessSetupDisks' (RHEL-131335)
- qemu: monitor: Extract block latency histogram stats into 'qemuBlockStats' (RHEL-131335)
- Expose latency histograms via 'virConnectGetAllDomainStats' (RHEL-131335)
- qemu: monitor: Add handlers for 'block-latency-histogram-set' (RHEL-131335)
- docs: formatdomain: Fix indentation of docs for <disk><driver><statistics> element (RHEL-131335)
- docs: formatdomain: Reword section about the '<statistics>' element under disk driver (RHEL-131335)
- Introduce support for disk operation latency histogram collection (RHEL-131335)
- qemu: Setup disk latency histograms on startup/hotplug/update (RHEL-131335)

Resolves: RHEL-131335, RHEL-135115
2026-02-17 14:58:02 +01:00

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From 8fbea435edb1635ec98c9419e9249223e5c3b2b6 Mon Sep 17 00:00:00 2001
Message-ID: <8fbea435edb1635ec98c9419e9249223e5c3b2b6.1771336682.git.jdenemar@redhat.com>
From: Peter Krempa <pkrempa@redhat.com>
Date: Fri, 23 Jan 2026 17:09:27 +0100
Subject: [PATCH] Introduce support for disk operation latency histogram
collection
Add config and docs allowing enabling latency histogram collection for
block device operations.
This patch sets up the docs, schema and XML infrastructure.
Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
(cherry picked from commit b874c944bd8c4ffa6c51394557587c8c203f1656)
https://issues.redhat.com/browse/RHEL-147866 [rhel-9.8]
https://issues.redhat.com/browse/RHEL-131335 [rhel-10.2]
---
docs/formatdomain.rst | 41 ++++++
src/conf/domain_conf.c | 133 +++++++++++++++++-
src/conf/domain_conf.h | 7 +
src/conf/schemas/domaincommon.rng | 37 ++++-
...isk-statistics-intervals.x86_64-latest.xml | 29 ++++
.../disk-statistics-intervals.xml | 25 ++++
6 files changed, 262 insertions(+), 10 deletions(-)
diff --git a/docs/formatdomain.rst b/docs/formatdomain.rst
index 70882c6820..31232deb3c 100644
--- a/docs/formatdomain.rst
+++ b/docs/formatdomain.rst
@@ -3628,6 +3628,47 @@ paravirtualized driver is specified via the ``disk`` element.
:since:`Since 11.9.0 (QEMU 10.2, virtio, ide, scsi disks only)`.
+ Block operation latency histogram collection can be configured using
+ ``<latency-histogram>`` sub-element. The histogram is collected for
+ the whole runtime of the VM, but can be re-started or reconfigured using
+ the `virDomainUpdateDeviceFlags <html/libvirt-libvirt-domain.html#virDomainUpdateDeviceFlags>`__
+ API. Using the same config re-starts histogram collection.
+
+ The optional ``type`` attribute configures specific operation to collect
+ the histogram for. Supported types are ``read``, ``write``, ``zone``, and
+ ``flush``. If the ``type`` attribute is omitted the histogram collection
+ bins bins apply to all of the aforementioned types, which can be overriden
+ with specific config.
+
+ The ``<latency-histogram>`` has multiple mandatory ``<bin>`` sub-elements
+ with mandatory ``start`` attribute configuring the starting boundary of
+ the histogram bin configured in nanosecods of the operation duration and
+ the intervals must be properly ordered and non-duplicate.
+
+ Example::
+
+ <driver name='qemu'>
+ <statistics>
+
+ <latency-histogram>
+ <bin start='0'/>
+ <bin start='1000'/>
+ <bin start='100000'/>
+ </latency-histogram>
+
+ [or for specific operation types]
+
+ <latency-histogram type='read'>
+ <bin start='0'/>
+ <bin start='1000'/>
+ <bin start='100000'/>
+ </latency-histogram>
+
+ </statistics>
+ </driver>
+
+ :since:`Since 12.1.0`.
+
- The optional ``queues`` attribute specifies the number of virt queues for
virtio-blk ( :since:`Since 3.9.0` ) or vhost-user-blk
( :since:`Since 7.1.0` )
diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
index f5c4d135a9..83c58ab5ff 100644
--- a/src/conf/domain_conf.c
+++ b/src/conf/domain_conf.c
@@ -2445,6 +2445,11 @@ virDomainDiskDefFree(virDomainDiskDef *def)
virObjectUnref(def->privateData);
g_slist_free_full(def->iothreads, (GDestroyNotify) virDomainIothreadMappingDefFree);
g_free(def->statistics);
+ g_free(def->histogram_boundaries);
+ g_free(def->histogram_boundaries_read);
+ g_free(def->histogram_boundaries_write);
+ g_free(def->histogram_boundaries_zone);
+ g_free(def->histogram_boundaries_flush);
if (def->throttlefilters) {
size_t i;
@@ -8307,6 +8312,91 @@ virDomainIothreadMappingDefParse(xmlNodePtr driverNode,
}
+static int
+virDomainDiskDefDriverParseXMLHistogramOne(virDomainDiskDef *def,
+ xmlNodePtr cur)
+{
+ g_autofree char *histogram_type = NULL;
+ unsigned int **histogram_config = NULL;
+ g_autoptr(GPtrArray) binNodes = virXMLNodeGetSubelementList(cur, "bin");
+ size_t nbins = 0;
+ size_t i;
+
+ if ((histogram_type = virXMLPropString(cur, "type"))) {
+ if (STREQ(histogram_type, "read")) {
+ histogram_config = &def->histogram_boundaries_read;
+ } else if (STREQ(histogram_type, "write")) {
+ histogram_config = &def->histogram_boundaries_write;
+ } else if (STREQ(histogram_type, "zone")) {
+ histogram_config = &def->histogram_boundaries_zone;
+ } else if (STREQ(histogram_type, "flush")) {
+ histogram_config = &def->histogram_boundaries_flush;
+ } else {
+ virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+ _("unknown latency_histogram type '%1$s'"),
+ histogram_type);
+ return -1;
+ }
+ } else {
+ histogram_config = &def->histogram_boundaries;
+ }
+
+ if (*histogram_config) {
+ virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+ _("only one latency-histogram of a given type is supported"));
+ return -1;
+ }
+
+ if (binNodes->len == 0) {
+ virReportError(VIR_ERR_XML_ERROR, "%s",
+ _("missing 'bin' elements for 'latency-histogram'"));
+ return -1;
+ }
+
+ *histogram_config = g_new0(unsigned int, binNodes->len + 1);
+
+ for (i = 0; i < binNodes->len; i++) {
+ unsigned int val;
+
+ if (virXMLPropUInt(g_ptr_array_index(binNodes, i),
+ "start", 10,
+ VIR_XML_PROP_REQUIRED,
+ &val) < 0)
+ return -1;
+
+ if (nbins > 0 &&
+ (val == 0 ||
+ val <= (*histogram_config)[nbins-1])) {
+ virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+ _("the values of 'start' attribute of a 'latency-histogram' 'bin' configuration must be sorted and non-overlapping"));
+ return -1;
+ }
+
+ if (val > 0)
+ (*histogram_config)[nbins++] = val;
+ }
+
+ return 0;
+}
+
+
+static int
+virDomainDiskDefDriverParseXMLHistograms(virDomainDiskDef *def,
+ xmlNodePtr cur)
+{
+ g_autoptr(GPtrArray) histogramNodes = virXMLNodeGetSubelementList(cur, "latency-histogram");
+ size_t i;
+
+ for (i = 0; i < histogramNodes->len; i++) {
+ if (virDomainDiskDefDriverParseXMLHistogramOne(def,
+ g_ptr_array_index(histogramNodes, i)) < 0)
+ return -1;
+ }
+
+ return 0;
+}
+
+
static int
virDomainDiskDefDriverParseXML(virDomainDiskDef *def,
xmlNodePtr cur)
@@ -8380,6 +8470,9 @@ virDomainDiskDefDriverParseXML(virDomainDiskDef *def,
return -1;
}
}
+
+ if (virDomainDiskDefDriverParseXMLHistograms(def, statisticsNode) < 0)
+ return -1;
}
if (virXMLPropEnum(cur, "detect_zeroes",
@@ -23961,12 +24054,37 @@ virDomainDiskDefFormatThrottleFilters(virBuffer *buf,
}
+static void
+virDomainDiskDefFormatDriverHistogram(virBuffer *buf,
+ const char *type,
+ unsigned int *bins)
+{
+ g_auto(virBuffer) histogramAttrBuf = VIR_BUFFER_INITIALIZER;
+ g_auto(virBuffer) histogramChildBuf = VIR_BUFFER_INIT_CHILD(buf);
+
+ if (!bins || bins[0] == 0)
+ return;
+
+ if (type)
+ virBufferAsprintf(&histogramAttrBuf, " type='%s'", type);
+
+ /* we dont store the start boundary of the first bin but it's always there */
+ virBufferAddLit(&histogramChildBuf, "<bin start='0'/>\n");
+
+ for (; *bins > 0; bins++)
+ virBufferAsprintf(&histogramChildBuf, "<bin start='%u'/>\n", *bins);
+
+ virXMLFormatElement(buf, "latency-histogram", &histogramAttrBuf, &histogramChildBuf);
+}
+
+
static void
virDomainDiskDefFormatDriver(virBuffer *buf,
virDomainDiskDef *disk)
{
g_auto(virBuffer) attrBuf = VIR_BUFFER_INITIALIZER;
g_auto(virBuffer) childBuf = VIR_BUFFER_INIT_CHILD(buf);
+ g_auto(virBuffer) statisticsChildBuf = VIR_BUFFER_INIT_CHILD(&childBuf);
virBufferEscapeString(&attrBuf, " name='%s'", virDomainDiskGetDriver(disk));
@@ -24038,16 +24156,25 @@ virDomainDiskDefFormatDriver(virBuffer *buf,
virDomainIothreadMappingDefFormat(&childBuf, disk->iothreads);
if (disk->statistics) {
- g_auto(virBuffer) statisticsChildBuf = VIR_BUFFER_INIT_CHILD(&childBuf);
size_t i;
for (i = 0; disk->statistics[i] > 0; i++)
virBufferAsprintf(&statisticsChildBuf, "<statistic interval='%u'/>\n",
disk->statistics[i]);
-
- virXMLFormatElement(&childBuf, "statistics", NULL, &statisticsChildBuf);
}
+ virDomainDiskDefFormatDriverHistogram(&statisticsChildBuf, NULL,
+ disk->histogram_boundaries);
+ virDomainDiskDefFormatDriverHistogram(&statisticsChildBuf, "read",
+ disk->histogram_boundaries_read);
+ virDomainDiskDefFormatDriverHistogram(&statisticsChildBuf, "write",
+ disk->histogram_boundaries_write);
+ virDomainDiskDefFormatDriverHistogram(&statisticsChildBuf, "zone",
+ disk->histogram_boundaries_zone);
+ virDomainDiskDefFormatDriverHistogram(&statisticsChildBuf, "flush",
+ disk->histogram_boundaries_flush);
+
+ virXMLFormatElement(&childBuf, "statistics", NULL, &statisticsChildBuf);
virXMLFormatElement(buf, "driver", &attrBuf, &childBuf);
}
diff --git a/src/conf/domain_conf.h b/src/conf/domain_conf.h
index 8f53ed96c0..b120d4a68e 100644
--- a/src/conf/domain_conf.h
+++ b/src/conf/domain_conf.h
@@ -596,6 +596,13 @@ struct _virDomainDiskDef {
GSList *iothreads; /* List of virDomainIothreadMappingDef */
unsigned int *statistics; /* Optional, zero terminated list of intervals to
collect statistics for */
+ /* optional zero terminated lists of bin boundaries for latency histograms */
+ unsigned int *histogram_boundaries;
+ unsigned int *histogram_boundaries_read;
+ unsigned int *histogram_boundaries_write;
+ unsigned int *histogram_boundaries_zone;
+ unsigned int *histogram_boundaries_flush;
+
virDomainDiskDetectZeroes detect_zeroes;
virTristateSwitch discard_no_unref;
char *domain_name; /* backend domain name */
diff --git a/src/conf/schemas/domaincommon.rng b/src/conf/schemas/domaincommon.rng
index 1f9ac102a0..441328a08e 100644
--- a/src/conf/schemas/domaincommon.rng
+++ b/src/conf/schemas/domaincommon.rng
@@ -2728,13 +2728,36 @@
</optional>
<optional>
<element name="statistics">
- <zeroOrMore>
- <element name="statistic">
- <attribute name="interval">
- <ref name="unsignedInt"/>
- </attribute>
- </element>
- </zeroOrMore>
+ <interleave>
+ <zeroOrMore>
+ <element name="statistic">
+ <attribute name="interval">
+ <ref name="unsignedInt"/>
+ </attribute>
+ </element>
+ </zeroOrMore>
+ <zeroOrMore>
+ <element name="latency-histogram">
+ <optional>
+ <attribute name='type'>
+ <choice>
+ <value>read</value>
+ <value>write</value>
+ <value>zone</value>
+ <value>flush</value>
+ </choice>
+ </attribute>
+ </optional>
+ <oneOrMore>
+ <element name='bin'>
+ <attribute name='start'>
+ <ref name="unsignedInt"/>
+ </attribute>
+ </element>
+ </oneOrMore>
+ </element>
+ </zeroOrMore>
+ </interleave>
</element>
</optional>
</interleave>
diff --git a/tests/qemuxmlconfdata/disk-statistics-intervals.x86_64-latest.xml b/tests/qemuxmlconfdata/disk-statistics-intervals.x86_64-latest.xml
index 4c55c50ef5..d02f954073 100644
--- a/tests/qemuxmlconfdata/disk-statistics-intervals.x86_64-latest.xml
+++ b/tests/qemuxmlconfdata/disk-statistics-intervals.x86_64-latest.xml
@@ -22,6 +22,11 @@
<statistics>
<statistic interval='3'/>
<statistic interval='10'/>
+ <latency-histogram>
+ <bin start='0'/>
+ <bin start='20'/>
+ <bin start='30'/>
+ </latency-histogram>
</statistics>
</driver>
<source file='/var/lib/libvirt/images/iothrtest1.img'/>
@@ -33,6 +38,30 @@
<statistics>
<statistic interval='5'/>
<statistic interval='15'/>
+ <latency-histogram type='read'>
+ <bin start='0'/>
+ <bin start='10'/>
+ <bin start='20'/>
+ <bin start='30'/>
+ </latency-histogram>
+ <latency-histogram type='write'>
+ <bin start='0'/>
+ <bin start='10'/>
+ <bin start='20'/>
+ <bin start='30'/>
+ </latency-histogram>
+ <latency-histogram type='zone'>
+ <bin start='0'/>
+ <bin start='10'/>
+ <bin start='20'/>
+ <bin start='30'/>
+ </latency-histogram>
+ <latency-histogram type='flush'>
+ <bin start='0'/>
+ <bin start='10'/>
+ <bin start='20'/>
+ <bin start='30'/>
+ </latency-histogram>
</statistics>
</driver>
<source file='/var/lib/libvirt/images/iothrtest2.img'/>
diff --git a/tests/qemuxmlconfdata/disk-statistics-intervals.xml b/tests/qemuxmlconfdata/disk-statistics-intervals.xml
index f5e801f5a8..5f9e9470d7 100644
--- a/tests/qemuxmlconfdata/disk-statistics-intervals.xml
+++ b/tests/qemuxmlconfdata/disk-statistics-intervals.xml
@@ -19,6 +19,11 @@
<statistics>
<statistic interval='3'/>
<statistic interval='10'/>
+ <latency-histogram>
+ <bin start='0'/>
+ <bin start='20'/>
+ <bin start='30'/>
+ </latency-histogram>
</statistics>
</driver>
<source file='/var/lib/libvirt/images/iothrtest1.img'/>
@@ -29,6 +34,26 @@
<statistics>
<statistic interval='5'/>
<statistic interval='15'/>
+ <latency-histogram type='read'>
+ <bin start='10'/>
+ <bin start='20'/>
+ <bin start='30'/>
+ </latency-histogram>
+ <latency-histogram type='write'>
+ <bin start='10'/>
+ <bin start='20'/>
+ <bin start='30'/>
+ </latency-histogram>
+ <latency-histogram type='zone'>
+ <bin start='10'/>
+ <bin start='20'/>
+ <bin start='30'/>
+ </latency-histogram>
+ <latency-histogram type='flush'>
+ <bin start='10'/>
+ <bin start='20'/>
+ <bin start='30'/>
+ </latency-histogram>
</statistics>
</driver>
<source file='/var/lib/libvirt/images/iothrtest2.img'/>
--
2.53.0
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