Re: [libvirt PATCH 1/2] qemu: support kvm-poll-control performance hint

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&gt; --- 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;