2:49 a.m.
QEMU version 4.2 introduced a performance feature under commit
d645e13287 ("kvm: i386: halt poll control MSR support").
This patch adds a new KVM feature 'poll-control' to set this performance
hint for KVM guests. The feature is off by default.
To enable this hint and have libvirt add "-cpu host,kvm-poll-control=on"
to the QEMU command line, the following XML code needs to be added to the
guest's domain description:
<features>
<kvm>
<poll-control state='on'/>
</kvm>
</features>
Signed-off-by: Tim Wiederhake <twiederh(a)redhat.com>
---
docs/formatdomain.rst | 14 ++++++++------
docs/schemas/domaincommon.rng | 5 +++++
src/conf/domain_conf.c | 4 ++++
src/conf/domain_conf.h | 1 +
src/qemu/qemu_command.c | 5 +++++
5 files changed, 23 insertions(+), 6 deletions(-)
diff --git a/docs/formatdomain.rst b/docs/formatdomain.rst
index a6ab845f92..cd5d7aae56 100644
--- a/docs/formatdomain.rst
+++ b/docs/formatdomain.rst
@@ -1766,6 +1766,7 @@ Hypervisors may allow certain CPU / machine features to be toggled
on/off.
<kvm>
<hidden state='on'/>
<hint-dedicated state='on'/>
+ <poll-control='on'/>
</kvm>
<xen>
<e820_host state='on'/>
@@ -1848,12 +1849,13 @@ are:
``kvm``
Various features to change the behavior of the KVM hypervisor.
- ============== ======================================================================
======= ============================
- Feature Description
Value Since
- ============== ======================================================================
======= ============================
- hidden Hide the KVM hypervisor from standard MSR based discovery
on, off :since:`1.2.8 (QEMU 2.1.0)`
- hint-dedicated Allows a guest to enable optimizations when running on dedicated vCPUs
on, off :since:`5.7.0 (QEMU 2.12.0)`
- ============== ======================================================================
======= ============================
+ ==============
============================================================================ =======
============================
+ Feature Description
Value Since
+ ==============
============================================================================ =======
============================
+ hidden Hide the KVM hypervisor from standard MSR based discovery
on, off :since:`1.2.8 (QEMU 2.1.0)`
+ hint-dedicated Allows a guest to enable optimizations when running on dedicated vCPUs
on, off :since:`5.7.0 (QEMU 2.12.0)`
+ poll-control Decrease IO completion latency by introducing a grace period of busy
waiting on, off :since:`6.11.0 (QEMU 4.2)`
+ ==============
============================================================================ =======
============================
``xen``
Various features to change the behavior of the Xen hypervisor.
diff --git a/docs/schemas/domaincommon.rng b/docs/schemas/domaincommon.rng
index e0d09f9c03..f86a854863 100644
--- a/docs/schemas/domaincommon.rng
+++ b/docs/schemas/domaincommon.rng
@@ -6512,6 +6512,11 @@
<ref name="featurestate"/>
</element>
</optional>
+ <optional>
+ <element name="poll-control">
+ <ref name="featurestate"/>
+ </element>
+ </optional>
</interleave>
</element>
</define>
diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
index 9199771dc0..2b56993845 100644
--- a/src/conf/domain_conf.c
+++ b/src/conf/domain_conf.c
@@ -208,6 +208,7 @@ VIR_ENUM_IMPL(virDomainKVM,
VIR_DOMAIN_KVM_LAST,
"hidden",
"hint-dedicated",
+ "poll-control",
);
VIR_ENUM_IMPL(virDomainXen,
@@ -19823,6 +19824,7 @@ virDomainFeaturesDefParse(virDomainDefPtr def,
switch ((virDomainKVM) feature) {
case VIR_DOMAIN_KVM_HIDDEN:
case VIR_DOMAIN_KVM_DEDICATED:
+ case VIR_DOMAIN_KVM_POLLCONTROL:
if (!(tmp = virXMLPropString(nodes[i], "state"))) {
virReportError(VIR_ERR_XML_ERROR,
_("missing 'state' attribute for
"
@@ -23982,6 +23984,7 @@ virDomainDefFeaturesCheckABIStability(virDomainDefPtr src,
switch ((virDomainKVM) i) {
case VIR_DOMAIN_KVM_HIDDEN:
case VIR_DOMAIN_KVM_DEDICATED:
+ case VIR_DOMAIN_KVM_POLLCONTROL:
if (src->kvm_features[i] != dst->kvm_features[i]) {
virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
_("State of KVM feature '%s' differs:
"
@@ -29695,6 +29698,7 @@ virDomainDefFormatFeatures(virBufferPtr buf,
switch ((virDomainKVM) j) {
case VIR_DOMAIN_KVM_HIDDEN:
case VIR_DOMAIN_KVM_DEDICATED:
+ case VIR_DOMAIN_KVM_POLLCONTROL:
if (def->kvm_features[j])
virBufferAsprintf(&childBuf, "<%s
state='%s'/>\n",
virDomainKVMTypeToString(j),
diff --git a/src/conf/domain_conf.h b/src/conf/domain_conf.h
index 16c050a3ea..3e3d4bd002 100644
--- a/src/conf/domain_conf.h
+++ b/src/conf/domain_conf.h
@@ -1912,6 +1912,7 @@ typedef enum {
typedef enum {
VIR_DOMAIN_KVM_HIDDEN = 0,
VIR_DOMAIN_KVM_DEDICATED,
+ VIR_DOMAIN_KVM_POLLCONTROL,
VIR_DOMAIN_KVM_LAST
} virDomainKVM;
diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
index 0eec35da16..34b5746c1a 100644
--- a/src/qemu/qemu_command.c
+++ b/src/qemu/qemu_command.c
@@ -6464,6 +6464,11 @@ qemuBuildCpuCommandLine(virCommandPtr cmd,
virBufferAddLit(&buf, ",kvm-hint-dedicated=on");
break;
+ case VIR_DOMAIN_KVM_POLLCONTROL:
+ if (def->kvm_features[i] == VIR_TRISTATE_SWITCH_ON)
+ virBufferAddLit(&buf, ",kvm-poll-control=on");
+ break;
+
/* coverity[dead_error_begin] */
case VIR_DOMAIN_KVM_LAST:
break;
--
2.26.2