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qemu: support kvm-poll-control performance hint

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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@redhat.com>
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
This commit is contained in:
Tim Wiederhake 2020-11-13 09:49:43 +01:00 committed by Michal Privoznik
parent 7e67a136da
commit 3fc4412c6f
5 changed files with 23 additions and 6 deletions
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14
docs/formatdomain.rst
View File

@ -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:`6.10.0 (QEMU 4.2)`
============== ============================================================================ ======= ============================
``xen``
Various features to change the behavior of the Xen hypervisor.

5
docs/schemas/domaincommon.rng
View File

@ -6512,6 +6512,11 @@
<ref name="featurestate"/>
</element>
</optional>
<optional>
<element name="poll-control">
<ref name="featurestate"/>
</element>
</optional>
</interleave>
</element>
</define>

4
src/conf/domain_conf.c
View File

@ -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: "
@ -29691,6 +29694,7 @@ 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),

1
src/conf/domain_conf.h
View File

@ -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;

5
src/qemu/qemu_command.c
View File

@ -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;