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[libvirt] [PATCH RFC 3/3] qemu: Add support for paravirtual spinlocks in the guest



The linux kernel recently added support for paravirtual spinlock
handling to avoid performance regressions on overcomitted hosts. This
feature needs to be turned in the hypervisor so that the guest OS is
notified about the possible support.

This patch adds a new feature "paravirt-spinlock" to the XML and
supporting code to enable the "kvm_pv_unhalt" pseudoCPU feature in qemu.

https://bugzilla.redhat.com/show_bug.cgi?id=1008989
---
This patch is RFC as qemu didn't add this to the upstream repo yet:

Pull request:
http://lists.nongnu.org/archive/html/qemu-devel/2013-09/msg03385.html

Original thread:
http://lists.nongnu.org/archive/html/qemu-devel/2013-09/msg03095.html

I'm sending it to get review feedback but will push it only after qemu will
have it.


 docs/formatdomain.html.in                          |  7 ++++++
 docs/schemas/domaincommon.rng                      | 10 ++++++++-
 src/conf/domain_conf.c                             | 20 ++++++++++++++++-
 src/conf/domain_conf.h                             |  1 +
 src/qemu/qemu_command.c                            | 14 ++++++++++++
 .../qemuxml2argv-pv-spinlock-disabled.args         |  5 +++++
 .../qemuxml2argv-pv-spinlock-disabled.xml          | 26 ++++++++++++++++++++++
 .../qemuxml2argv-pv-spinlock-enabled.args          |  5 +++++
 .../qemuxml2argv-pv-spinlock-enabled.xml           | 26 ++++++++++++++++++++++
 tests/qemuxml2argvtest.c                           |  2 ++
 tests/qemuxml2xmltest.c                            |  2 ++
 11 files changed, 116 insertions(+), 2 deletions(-)
 create mode 100644 tests/qemuxml2argvdata/qemuxml2argv-pv-spinlock-disabled.args
 create mode 100644 tests/qemuxml2argvdata/qemuxml2argv-pv-spinlock-disabled.xml
 create mode 100644 tests/qemuxml2argvdata/qemuxml2argv-pv-spinlock-enabled.args
 create mode 100644 tests/qemuxml2argvdata/qemuxml2argv-pv-spinlock-enabled.xml

diff --git a/docs/formatdomain.html.in b/docs/formatdomain.html.in
index 3689399..aa0076c 100644
--- a/docs/formatdomain.html.in
+++ b/docs/formatdomain.html.in
@@ -1182,6 +1182,7 @@
       <vapic state='on'/>
       <spinlocks state='on' retries='4096'/>
     </hyperv>
+    <paravirt-spinlock/>

   </features>
   ...</pre>
@@ -1253,6 +1254,12 @@
         </tr>
       </table>
       </dd>
+      <dt><code>paravirtual-spinlock</code></dt>
+      <dd>Notify the guest that the host supports paravirtual spinlocks
+          for example by exposing the pvticketlocks mechanism. This feature
+          can be forced of by using a "state='off'" attribute.
+      </dd>
+
     </dl>

     <h3><a name="elementsTime">Time keeping</a></h3>
diff --git a/docs/schemas/domaincommon.rng b/docs/schemas/domaincommon.rng
index 94a72f8..4c494cb 100644
--- a/docs/schemas/domaincommon.rng
+++ b/docs/schemas/domaincommon.rng
@@ -3560,7 +3560,7 @@
   </define>
   <!--
       A set of optional features: PAE, APIC, ACPI,
-      HyperV Enlightenment and HAP support
+      HyperV Enlightenment, paravirtual spinlocks  and HAP support
     -->
   <define name="features">
     <optional>
@@ -3606,6 +3606,14 @@
               <empty/>
             </element>
           </optional>
+          <optional>
+            <element name="paravirt-spinlock">
+              <optional>
+                <ref name="featurestate"/>
+              </optional>
+              <empty/>
+            </element>
+          </optional>
         </interleave>
       </element>
     </optional>
diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
index e1a1d6d..919adc1 100644
--- a/src/conf/domain_conf.c
+++ b/src/conf/domain_conf.c
@@ -142,7 +142,8 @@ VIR_ENUM_IMPL(virDomainFeature, VIR_DOMAIN_FEATURE_LAST,
               "hap",
               "viridian",
               "privnet",
-              "hyperv")
+              "hyperv",
+              "paravirt-spinlock")

 VIR_ENUM_IMPL(virDomainFeatureState, VIR_DOMAIN_FEATURE_STATE_LAST,
               "default",
@@ -11394,6 +11395,22 @@ virDomainDefParseXML(xmlDocPtr xml,
             def->features[val] = VIR_DOMAIN_FEATURE_STATE_ON;
             break;

+        case VIR_DOMAIN_FEATURE_PARAVIRT_SPINLOCK:
+            node = ctxt->node;
+            ctxt->node = nodes[i];
+            if ((tmp = virXPathString("string(./@state)", ctxt))) {
+                if ((def->features[val] = virDomainFeatureStateTypeFromString(tmp)) == -1) {
+                    virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                                   _("unknown state atribute '%s' of feature '%s'"),
+                                   tmp, virDomainFeatureTypeToString(val));
+                    goto error;
+                }
+            } else {
+                def->features[val] = VIR_DOMAIN_FEATURE_STATE_ON;
+            }
+            ctxt->node = node;
+            break;
+
         case VIR_DOMAIN_FEATURE_LAST:
             break;
         }
@@ -16742,6 +16759,7 @@ virDomainDefFormatInternal(virDomainDefPtr def,
             case VIR_DOMAIN_FEATURE_HAP:
             case VIR_DOMAIN_FEATURE_VIRIDIAN:
             case VIR_DOMAIN_FEATURE_PRIVNET:
+            case VIR_DOMAIN_FEATURE_PARAVIRT_SPINLOCK:
                 switch ((enum virDomainFeatureState) def->features[i]) {
                 case VIR_DOMAIN_FEATURE_STATE_ON:
                     /* output just the element */
diff --git a/src/conf/domain_conf.h b/src/conf/domain_conf.h
index 9ddd706..4d69c4f 100644
--- a/src/conf/domain_conf.h
+++ b/src/conf/domain_conf.h
@@ -1618,6 +1618,7 @@ enum virDomainFeature {
     VIR_DOMAIN_FEATURE_VIRIDIAN,
     VIR_DOMAIN_FEATURE_PRIVNET,
     VIR_DOMAIN_FEATURE_HYPERV,
+    VIR_DOMAIN_FEATURE_PARAVIRT_SPINLOCK,

     VIR_DOMAIN_FEATURE_LAST
 };
diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
index 6f3b3cb..01de440 100644
--- a/src/qemu/qemu_command.c
+++ b/src/qemu/qemu_command.c
@@ -6608,6 +6608,20 @@ qemuBuildCpuArgStr(const virQEMUDriverPtr driver,
         have_cpu = true;
     }

+    if (def->features[VIR_DOMAIN_FEATURE_PARAVIRT_SPINLOCK]) {
+        char sign;
+        if (def->features[VIR_DOMAIN_FEATURE_PARAVIRT_SPINLOCK] ==
+            VIR_DOMAIN_FEATURE_STATE_ON)
+            sign = '+';
+        else
+            sign = '-';
+
+        virBufferAsprintf(&buf, "%s,%ckvm_pv_unhalt",
+                          have_cpu ? "" : default_model,
+                          sign);
+        have_cpu = true;
+    }
+
     if (def->features[VIR_DOMAIN_FEATURE_HYPERV] == VIR_DOMAIN_FEATURE_STATE_ON) {
         if (!have_cpu) {
             virBufferAdd(&buf, default_model, -1);
diff --git a/tests/qemuxml2argvdata/qemuxml2argv-pv-spinlock-disabled.args b/tests/qemuxml2argvdata/qemuxml2argv-pv-spinlock-disabled.args
new file mode 100644
index 0000000..80047f9
--- /dev/null
+++ b/tests/qemuxml2argvdata/qemuxml2argv-pv-spinlock-disabled.args
@@ -0,0 +1,5 @@
+LC_ALL=C PATH=/bin HOME=/home/test USER=test LOGNAME=test QEMU_AUDIO_DRV=none \
+/usr/bin/qemu -S -M pc \
+-cpu qemu32,-kvm_pv_unhalt -m 214 -smp 6 -nographic -monitor \
+unix:/tmp/test-monitor,server,nowait -boot n -usb -net none -serial \
+none -parallel none
diff --git a/tests/qemuxml2argvdata/qemuxml2argv-pv-spinlock-disabled.xml b/tests/qemuxml2argvdata/qemuxml2argv-pv-spinlock-disabled.xml
new file mode 100644
index 0000000..afb0b41
--- /dev/null
+++ b/tests/qemuxml2argvdata/qemuxml2argv-pv-spinlock-disabled.xml
@@ -0,0 +1,26 @@
+<domain type='qemu'>
+  <name>QEMUGuest1</name>
+  <uuid>c7a5fdbd-edaf-9455-926a-d65c16db1809</uuid>
+  <memory unit='KiB'>219100</memory>
+  <currentMemory unit='KiB'>219100</currentMemory>
+  <vcpu placement='static'>6</vcpu>
+  <os>
+    <type arch='i686' machine='pc'>hvm</type>
+    <boot dev='network'/>
+  </os>
+  <features>
+    <acpi/>
+    <pae/>
+    <paravirt-spinlock state='off'/>
+  </features>
+  <clock offset='utc'/>
+  <on_poweroff>destroy</on_poweroff>
+  <on_reboot>restart</on_reboot>
+  <on_crash>destroy</on_crash>
+  <devices>
+    <emulator>/usr/bin/qemu</emulator>
+    <controller type='usb' index='0'/>
+    <controller type='pci' index='0' model='pci-root'/>
+    <memballoon model='virtio'/>
+  </devices>
+</domain>
diff --git a/tests/qemuxml2argvdata/qemuxml2argv-pv-spinlock-enabled.args b/tests/qemuxml2argvdata/qemuxml2argv-pv-spinlock-enabled.args
new file mode 100644
index 0000000..70db173
--- /dev/null
+++ b/tests/qemuxml2argvdata/qemuxml2argv-pv-spinlock-enabled.args
@@ -0,0 +1,5 @@
+LC_ALL=C PATH=/bin HOME=/home/test USER=test LOGNAME=test QEMU_AUDIO_DRV=none \
+/usr/bin/qemu -S -M pc \
+-cpu qemu32,+kvm_pv_unhalt -m 214 -smp 6 -nographic -monitor \
+unix:/tmp/test-monitor,server,nowait -boot n -usb -net none -serial \
+none -parallel none
diff --git a/tests/qemuxml2argvdata/qemuxml2argv-pv-spinlock-enabled.xml b/tests/qemuxml2argvdata/qemuxml2argv-pv-spinlock-enabled.xml
new file mode 100644
index 0000000..f29cade
--- /dev/null
+++ b/tests/qemuxml2argvdata/qemuxml2argv-pv-spinlock-enabled.xml
@@ -0,0 +1,26 @@
+<domain type='qemu'>
+  <name>QEMUGuest1</name>
+  <uuid>c7a5fdbd-edaf-9455-926a-d65c16db1809</uuid>
+  <memory unit='KiB'>219100</memory>
+  <currentMemory unit='KiB'>219100</currentMemory>
+  <vcpu placement='static'>6</vcpu>
+  <os>
+    <type arch='i686' machine='pc'>hvm</type>
+    <boot dev='network'/>
+  </os>
+  <features>
+    <acpi/>
+    <pae/>
+    <paravirt-spinlock/>
+  </features>
+  <clock offset='utc'/>
+  <on_poweroff>destroy</on_poweroff>
+  <on_reboot>restart</on_reboot>
+  <on_crash>destroy</on_crash>
+  <devices>
+    <emulator>/usr/bin/qemu</emulator>
+    <controller type='usb' index='0'/>
+    <controller type='pci' index='0' model='pci-root'/>
+    <memballoon model='virtio'/>
+  </devices>
+</domain>
diff --git a/tests/qemuxml2argvtest.c b/tests/qemuxml2argvtest.c
index ec4a6e5..72b6b2a 100644
--- a/tests/qemuxml2argvtest.c
+++ b/tests/qemuxml2argvtest.c
@@ -435,6 +435,8 @@ mymain(void)
             QEMU_CAPS_CHARDEV_SPICEVMC, QEMU_CAPS_SPICE, QEMU_CAPS_HDA_DUPLEX);
     DO_TEST("eoi-disabled", NONE);
     DO_TEST("eoi-enabled", NONE);
+    DO_TEST("pv-spinlock-disabled", NONE);
+    DO_TEST("pv-spinlock-enabled", NONE);
     DO_TEST("kvmclock+eoi-disabled", QEMU_CAPS_ENABLE_KVM);

     DO_TEST("hyperv", NONE);
diff --git a/tests/qemuxml2xmltest.c b/tests/qemuxml2xmltest.c
index c661573..0e83dcf 100644
--- a/tests/qemuxml2xmltest.c
+++ b/tests/qemuxml2xmltest.c
@@ -156,6 +156,8 @@ mymain(void)
     DO_TEST("cpu-eoi-enabled");
     DO_TEST("eoi-disabled");
     DO_TEST("eoi-enabled");
+    DO_TEST("pv-spinlock-disabled");
+    DO_TEST("pv-spinlock-enabled");

     DO_TEST("hyperv");
     DO_TEST("hyperv-off");
-- 
1.8.3.2


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