conf: Add support for virtio-net.rx_queue_size

https://bugzilla.redhat.com/show_bug.cgi?id=1366989

QEMU added another virtio-net tunable [1]. It basically allows
users to set the size of RX virtio ring. But because virtio-net
uses two separate ring buffers to pass data from/to guest they
named it explicitly rx_queue_size. We should expose it in our XML
too.

1: http://lists.nongnu.org/archive/html/qemu-devel/2016-08/msg02029.html

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>

docs/formatdomain.html.in

@@ -4674,7 +4674,7 @@ qemu-kvm -net nic,model=? /dev/null
       <source network='default'/>
       <target dev='vnet1'/>
       <model type='virtio'/>
-      <b>&lt;driver name='vhost' txmode='iothread' ioeventfd='on' event_idx='off' queues='5'&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;/driver&gt;
@@ -4790,6 +4790,20 @@ qemu-kvm -net nic,model=? /dev/null
         <span class="since">virtio-net since 1.0.6 (QEMU and KVM only)</span>
         <span class="since">vhost-user since 1.2.17 (QEMU and KVM only)</span>
       </dd>
+      <dt><code>rx_queue_size</code></dt>
+      <dd>
+        The optional <code>rx_queue_size</code> attribute controls
+        the size of virtio ring for each queue as described above.
+        The default value is hypervisor dependent and may change
+        across its releases. Moreover, some hypervisors may pose
+        some restrictions on actual value. For instance, latest
+        QEMU (as of 2016-09-01) requires value to be a power of two
+        from [256, 1024] range.
+        <span class="since">Since 2.3.0 (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>
     </dl>
     <p>
       Offloading options for the host and guest can be configured using

docs/schemas/domaincommon.rng

@@ -2557,6 +2557,11 @@
                   <ref name="positiveInteger"/>
                 </attribute>
               </optional>
+              <optional>
+                <attribute name='rx_queue_size'>
+                  <ref name='positiveInteger'/>
+                </attribute>
+              </optional>
               <optional>
                 <attribute name="txmode">
                   <choice>

src/conf/domain_conf.c

@@ -8981,6 +8981,7 @@ virDomainNetDefParseXML(virDomainXMLOptionPtr xmlopt,
     char *ioeventfd = NULL;
     char *event_idx = NULL;
     char *queues = NULL;
+    char *rx_queue_size = NULL;
     char *str = NULL;
     char *filter = NULL;
     char *internal = NULL;
@@ -9153,6 +9154,7 @@ virDomainNetDefParseXML(virDomainXMLOptionPtr xmlopt,
                 ioeventfd = virXMLPropString(cur, "ioeventfd");
                 event_idx = virXMLPropString(cur, "event_idx");
                 queues = virXMLPropString(cur, "queues");
+                rx_queue_size = virXMLPropString(cur, "rx_queue_size");
             } else if (xmlStrEqual(cur->name, BAD_CAST "filterref")) {
                 if (filter) {
                     virReportError(VIR_ERR_XML_ERROR, "%s",
@@ -9536,6 +9538,16 @@ virDomainNetDefParseXML(virDomainXMLOptionPtr xmlopt,
             if (q > 1)
                 def->driver.virtio.queues = q;
         }
+        if (rx_queue_size) {
+            unsigned int q;
+            if (virStrToLong_uip(rx_queue_size, NULL, 10, &q) < 0) {
+                virReportError(VIR_ERR_XML_DETAIL,
+                               _("'rx_queue_size' attribute must be positive number: %s"),
+                               rx_queue_size);
+                goto error;
+            }
+            def->driver.virtio.rx_queue_size = q;
+        }
         if ((str = virXPathString("string(./driver/host/@csum)", ctxt))) {
             if ((val = virTristateSwitchTypeFromString(str)) <= 0) {
                 virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
@@ -9716,6 +9728,7 @@ virDomainNetDefParseXML(virDomainXMLOptionPtr xmlopt,
     VIR_FREE(ioeventfd);
     VIR_FREE(event_idx);
     VIR_FREE(queues);
+    VIR_FREE(rx_queue_size);
     VIR_FREE(str);
     VIR_FREE(filter);
     VIR_FREE(type);
@@ -20919,6 +20932,9 @@ virDomainVirtioNetDriverFormat(char **outstr,
     }
     if (def->driver.virtio.queues)
         virBufferAsprintf(&buf, "queues='%u' ", def->driver.virtio.queues);
+    if (def->driver.virtio.rx_queue_size)
+        virBufferAsprintf(&buf, "rx_queue_size='%u' ",
+                          def->driver.virtio.rx_queue_size);
 
     virBufferTrim(&buf, " ", -1);
 

src/conf/domain_conf.h

@@ -906,6 +906,7 @@ struct _virDomainNetDef {
             virTristateSwitch ioeventfd;
             virTristateSwitch event_idx;
             unsigned int queues; /* Multiqueue virtio-net */
+            unsigned int rx_queue_size;
             struct {
                 virTristateSwitch csum;
                 virTristateSwitch gso;

src/qemu/qemu_domain.c

@@ -2475,6 +2475,13 @@ qemuDomainDeviceDefValidate(const virDomainDeviceDef *dev,
                              "not supported by QEMU"));
             goto cleanup;
         }
+
+        if (STREQ_NULLABLE(net->model, "virtio") &&
+            net->driver.virtio.rx_queue_size & (net->driver.virtio.rx_queue_size - 1)) {
+            virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+                           _("rx_queue_size has to be a power of two"));
+            goto cleanup;
+        }
     }
 
     ret = 0;

tests/qemuxml2argvdata/qemuxml2argv-net-virtio-rxqueuesize-invalid-size.xml

@@ -0,0 +1,29 @@
+<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</emulator>
+    <disk type='block' device='disk'>
+      <source dev='/dev/HostVG/QEMUGuest1'/>
+      <target dev='hda' bus='ide'/>
+    </disk>
+    <controller type='usb' index='0'/>
+    <interface type='user'>
+      <mac address='00:11:22:33:44:55'/>
+      <model type='virtio'/>
+      <driver rx_queue_size='511'/>
+    </interface>
+    <memballoon model='virtio'/>
+  </devices>
+</domain>

tests/qemuxml2argvdata/qemuxml2argv-net-virtio-rxqueuesize.xml

@@ -0,0 +1,29 @@
+<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</emulator>
+    <disk type='block' device='disk'>
+      <source dev='/dev/HostVG/QEMUGuest1'/>
+      <target dev='hda' bus='ide'/>
+    </disk>
+    <controller type='usb' index='0'/>
+    <interface type='user'>
+      <mac address='00:11:22:33:44:55'/>
+      <model type='virtio'/>
+      <driver rx_queue_size='512'/>
+    </interface>
+    <memballoon model='virtio'/>
+  </devices>
+</domain>

tests/qemuxml2argvtest.c

@@ -1047,6 +1047,7 @@ mymain(void)
             QEMU_CAPS_VIRTIO_S390);
     DO_TEST("net-virtio-ccw",
             QEMU_CAPS_VIRTIO_CCW, QEMU_CAPS_VIRTIO_S390);
+    DO_TEST_PARSE_ERROR("net-virtio-rxqueuesize-invalid-size", NONE);
     DO_TEST("net-eth", NONE);
     DO_TEST("net-eth-ifname", NONE);
     DO_TEST("net-eth-names", NONE);

tests/qemuxml2xmloutdata/qemuxml2xmlout-net-virtio-rxqueuesize.xml

@@ -0,0 +1,41 @@
+<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</emulator>
+    <disk type='block' device='disk'>
+      <source dev='/dev/HostVG/QEMUGuest1'/>
+      <target dev='hda' bus='ide'/>
+      <address type='drive' controller='0' bus='0' target='0' unit='0'/>
+    </disk>
+    <controller type='usb' index='0'>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x2'/>
+    </controller>
+    <controller type='pci' index='0' model='pci-root'/>
+    <controller type='ide' index='0'>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x1'/>
+    </controller>
+    <interface type='user'>
+      <mac address='00:11:22:33:44:55'/>
+      <model type='virtio'/>
+      <driver rx_queue_size='512'/>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
+    </interface>
+    <input type='mouse' bus='ps2'/>
+    <input type='keyboard' bus='ps2'/>
+    <memballoon model='virtio'>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>
+    </memballoon>
+  </devices>
+</domain>

tests/qemuxml2xmltest.c

@@ -514,6 +514,7 @@ mymain(void)
     DO_TEST("net-eth-ifname", NONE);
     DO_TEST("net-eth-hostip", NONE);
     DO_TEST("net-virtio-network-portgroup", NONE);
+    DO_TEST("net-virtio-rxqueuesize", NONE);
     DO_TEST("net-hostdev", NONE);
     DO_TEST("net-hostdev-vfio", NONE);
     DO_TEST("net-midonet", NONE);