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[libvirt] [PATCH 3/3] qemu: add busy polling support



From: Sahid Orentino Ferdjaoui <sahid ferdjaoui redhat com>

This patch finalizes support of 'poll_us' attribute as an option of
the NIC driver-specific element, the commit also takes care of
hotplug.

<devices>
  <interface type='ethernet'>
    <mac address='52:54:00:23:bc:ba'/>
    <model type='virtio'/>
    <driver name="vhost" poll_us='50'/>
  </interface>
</devices>

That option is supported for all networks which are using a tap
device.

To be used the backend should be specificly set to use vhost.

Signed-off-by: Sahid Orentino Ferdjaoui <sahid ferdjaoui redhat com>
---
 docs/formatdomain.html.in                          | 12 ++++++++++-
 docs/schemas/domaincommon.rng                      |  5 +++++
 src/qemu/qemu_command.c                            | 22 +++++++++++++++++++++
 src/qemu/qemu_hotplug.c                            | 12 +++++++++++
 .../qemuxml2argv-net-virtio-netdev-pollus-fail.xml | 23 ++++++++++++++++++++++
 ...xml2argv-net-virtio-netdev-pollus-qemu-fail.xml | 23 ++++++++++++++++++++++
 .../qemuxml2argv-net-virtio-netdev-pollus.args     | 23 ++++++++++++++++++++++
 .../qemuxml2argv-net-virtio-netdev-pollus.xml      | 23 ++++++++++++++++++++++
 tests/qemuxml2argvtest.c                           |  9 +++++++++
 9 files changed, 151 insertions(+), 1 deletion(-)
 create mode 100644 tests/qemuxml2argvdata/qemuxml2argv-net-virtio-netdev-pollus-fail.xml
 create mode 100644 tests/qemuxml2argvdata/qemuxml2argv-net-virtio-netdev-pollus-qemu-fail.xml
 create mode 100644 tests/qemuxml2argvdata/qemuxml2argv-net-virtio-netdev-pollus.args
 create mode 100644 tests/qemuxml2argvdata/qemuxml2argv-net-virtio-netdev-pollus.xml

diff --git a/docs/formatdomain.html.in b/docs/formatdomain.html.in
index 52119f0..7bfeabc 100644
--- a/docs/formatdomain.html.in
+++ b/docs/formatdomain.html.in
@@ -5043,7 +5043,7 @@ qemu-kvm -net nic,model=? /dev/null
     &lt;model type='virtio'/&gt;
     <b>&lt;driver name='vhost' txmode='iothread' ioeventfd='on' event_idx='off' queues='5' rx_queue_size='256'&gt;
       &lt;host csum='off' gso='off' tso4='off' tso6='off' ecn='off' ufo='off' mrg_rxbuf='off'/&gt;
-      &lt;guest csum='off' tso4='off' tso6='off' ecn='off' ufo='off'/&gt;
+      &lt;guest csum='off' tso4='off' tso6='off' ecn='off' ufo='off' poll_us='50'/&gt;
     &lt;/driver&gt;
     </b>
   &lt;/interface&gt;
@@ -5171,6 +5171,16 @@ qemu-kvm -net nic,model=? /dev/null
         <b>In general you should leave this option alone, unless you
         are very certain you know what you are doing.</b>
       </dd>
+      <dd>
+        The optional <code>poll_us</code> attribute configure the
+        maximum number of microseconds that could be spent on busy
+        polling. It improves the performance, but requires more
+        CPU. This option is only available with vhost backend driver.
+        <span class="since">Since 2.7.0 (QEMU and KVM only)</span><br/><br/>
+
+        <b>In general you should leave this option alone, unless you
+        are very certain you know what you are doing.</b>
+      </dd>
       <dt>virtio options</dt>
       <dd>
         For virtio interfaces,
diff --git a/docs/schemas/domaincommon.rng b/docs/schemas/domaincommon.rng
index 4950ddc..f304385 100644
--- a/docs/schemas/domaincommon.rng
+++ b/docs/schemas/domaincommon.rng
@@ -2687,6 +2687,11 @@
               <optional>
                 <ref name="event_idx"/>
               </optional>
+              <optional>
+                <attribute name='poll_us'>
+                  <ref name='positiveInteger'/>
+                </attribute>
+              </optional>
             </group>
           </choice>
           <ref name="virtioOptions"/>
diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
index 8c12b2b..412496e 100644
--- a/src/qemu/qemu_command.c
+++ b/src/qemu/qemu_command.c
@@ -3955,6 +3955,9 @@ qemuBuildHostNetStr(virDomainNetDefPtr net,
         }
         if (net->tune.sndbuf_specified)
             virBufferAsprintf(&buf, "sndbuf=%lu,", net->tune.sndbuf);
+        if (net->driver.virtio.pollus)
+            virBufferAsprintf(&buf, "poll-us=%u,",
+                              net->driver.virtio.pollus);
     }
 
     virObjectUnref(cfg);
@@ -8451,6 +8454,25 @@ qemuBuildInterfaceCommandLine(virQEMUDriverPtr driver,
         return -1;
     }
 
+    if (net->driver.virtio.pollus > 0) {
+        if (net->driver.virtio.name != VIR_DOMAIN_NET_BACKEND_TYPE_VHOST) {
+            virReportError(
+                VIR_ERR_CONFIG_UNSUPPORTED,
+                _("Busy polling is only supported with vhost backend driver"));
+            return -1;
+        }
+        /* Nothing besides TAP devices supports busy polling. */
+        if (!(actualType == VIR_DOMAIN_NET_TYPE_NETWORK ||
+              actualType == VIR_DOMAIN_NET_TYPE_BRIDGE ||
+              actualType == VIR_DOMAIN_NET_TYPE_DIRECT ||
+              actualType == VIR_DOMAIN_NET_TYPE_ETHERNET)) {
+            virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                           _("Busy polling is not supported for: %s"),
+                           virDomainNetTypeToString(actualType));
+            return -1;
+        }
+    }
+
     /* and only TAP devices support nwfilter rules */
     if (net->filter &&
         !(actualType == VIR_DOMAIN_NET_TYPE_NETWORK ||
diff --git a/src/qemu/qemu_hotplug.c b/src/qemu/qemu_hotplug.c
index 0b8d3d8..33884b7 100644
--- a/src/qemu/qemu_hotplug.c
+++ b/src/qemu/qemu_hotplug.c
@@ -995,6 +995,18 @@ qemuDomainAttachNetDevice(virQEMUDriverPtr driver,
         return -1;
     }
 
+    /* and nothing besides TAP devices supports busy polling. */
+    if (net->driver.virtio.pollus > 0 &&
+        !(actualType == VIR_DOMAIN_NET_TYPE_NETWORK ||
+          actualType == VIR_DOMAIN_NET_TYPE_BRIDGE ||
+          actualType == VIR_DOMAIN_NET_TYPE_DIRECT ||
+          actualType == VIR_DOMAIN_NET_TYPE_ETHERNET)) {
+        virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                       _("Busy polling is not supported for: %s"),
+                       virDomainNetTypeToString(actualType));
+        return -1;
+    }
+
     /* and only TAP devices support nwfilter rules */
     if (net->filter &&
         !(actualType == VIR_DOMAIN_NET_TYPE_NETWORK ||
diff --git a/tests/qemuxml2argvdata/qemuxml2argv-net-virtio-netdev-pollus-fail.xml b/tests/qemuxml2argvdata/qemuxml2argv-net-virtio-netdev-pollus-fail.xml
new file mode 100644
index 0000000..3b664b9
--- /dev/null
+++ b/tests/qemuxml2argvdata/qemuxml2argv-net-virtio-netdev-pollus-fail.xml
@@ -0,0 +1,23 @@
+<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'>1</vcpu>
+  <os>
+    <type arch='i686' machine='pc'>hvm</type>
+    <boot dev='hd'/>
+  </os>
+  <clock offset='utc'/>
+  <on_poweroff>destroy</on_poweroff>
+  <on_reboot>restart</on_reboot>
+  <on_crash>destroy</on_crash>
+  <devices>
+    <emulator>/usr/bin/qemu-system-i686</emulator>
+    <interface type='ethernet'>
+      <mac address='52:54:00:23:bc:ba'/>
+      <model type='virtio'/>
+      <driver poll_us='50'/>
+    </interface>
+  </devices>
+</domain>
diff --git a/tests/qemuxml2argvdata/qemuxml2argv-net-virtio-netdev-pollus-qemu-fail.xml b/tests/qemuxml2argvdata/qemuxml2argv-net-virtio-netdev-pollus-qemu-fail.xml
new file mode 100644
index 0000000..18999c3
--- /dev/null
+++ b/tests/qemuxml2argvdata/qemuxml2argv-net-virtio-netdev-pollus-qemu-fail.xml
@@ -0,0 +1,23 @@
+<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'>1</vcpu>
+  <os>
+    <type arch='i686' machine='pc'>hvm</type>
+    <boot dev='hd'/>
+  </os>
+  <clock offset='utc'/>
+  <on_poweroff>destroy</on_poweroff>
+  <on_reboot>restart</on_reboot>
+  <on_crash>destroy</on_crash>
+  <devices>
+    <emulator>/usr/bin/qemu-system-i686</emulator>
+    <interface type='ethernet'>
+      <mac address='52:54:00:23:bc:ba'/>
+      <model type='virtio'/>
+      <driver name="qemu" poll_us='50'/>
+    </interface>
+  </devices>
+</domain>
diff --git a/tests/qemuxml2argvdata/qemuxml2argv-net-virtio-netdev-pollus.args b/tests/qemuxml2argvdata/qemuxml2argv-net-virtio-netdev-pollus.args
new file mode 100644
index 0000000..8d44134
--- /dev/null
+++ b/tests/qemuxml2argvdata/qemuxml2argv-net-virtio-netdev-pollus.args
@@ -0,0 +1,23 @@
+LC_ALL=C \
+PATH=/bin \
+HOME=/home/test \
+USER=test \
+LOGNAME=test \
+QEMU_AUDIO_DRV=none \
+/usr/bin/qemu-system-i686 \
+-name QEMUGuest1 \
+-S \
+-M pc \
+-m 214 \
+-smp 1,sockets=1,cores=1,threads=1 \
+-uuid c7a5fdbd-edaf-9455-926a-d65c16db1809 \
+-nographic \
+-nodefaults \
+-monitor unix:/tmp/lib/domain--1-QEMUGuest1/monitor.sock,server,nowait \
+-no-acpi \
+-boot c \
+-usb \
+-netdev tap,fd=3,id=hostnet0,poll-us=50 \
+-device virtio-net-pci,netdev=hostnet0,id=net0,mac=52:54:00:23:bc:ba,bus=pci.0,\
+addr=0x3 \
+-device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x4
diff --git a/tests/qemuxml2argvdata/qemuxml2argv-net-virtio-netdev-pollus.xml b/tests/qemuxml2argvdata/qemuxml2argv-net-virtio-netdev-pollus.xml
new file mode 100644
index 0000000..46ef7d6
--- /dev/null
+++ b/tests/qemuxml2argvdata/qemuxml2argv-net-virtio-netdev-pollus.xml
@@ -0,0 +1,23 @@
+<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'>1</vcpu>
+  <os>
+    <type arch='i686' machine='pc'>hvm</type>
+    <boot dev='hd'/>
+  </os>
+  <clock offset='utc'/>
+  <on_poweroff>destroy</on_poweroff>
+  <on_reboot>restart</on_reboot>
+  <on_crash>destroy</on_crash>
+  <devices>
+    <emulator>/usr/bin/qemu-system-i686</emulator>
+    <interface type='ethernet'>
+      <mac address='52:54:00:23:bc:ba'/>
+      <model type='virtio'/>
+      <driver name="vhost" poll_us='50'/>
+    </interface>
+  </devices>
+</domain>
diff --git a/tests/qemuxml2argvtest.c b/tests/qemuxml2argvtest.c
index 799aea9..54d1b07 100644
--- a/tests/qemuxml2argvtest.c
+++ b/tests/qemuxml2argvtest.c
@@ -1133,6 +1133,15 @@ mymain(void)
             QEMU_CAPS_NODEFCONFIG);
     DO_TEST("net-virtio-netdev",
             QEMU_CAPS_NETDEV, QEMU_CAPS_NODEFCONFIG);
+    DO_TEST("net-virtio-netdev-pollus",
+            QEMU_CAPS_NETDEV,
+            QEMU_CAPS_VHOST_NET_POLL_US);
+    DO_TEST_FAILURE("net-virtio-netdev-pollus-fail",
+                    QEMU_CAPS_NETDEV,
+                    QEMU_CAPS_VHOST_NET_POLL_US);
+    DO_TEST_FAILURE("net-virtio-netdev-pollus-qemu-fail",
+                    QEMU_CAPS_NETDEV,
+                    QEMU_CAPS_VHOST_NET_POLL_US);
     DO_TEST("net-virtio-s390",
             QEMU_CAPS_VIRTIO_S390);
     DO_TEST("net-virtio-ccw",
-- 
2.9.4


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