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Add txmode attribute to interface XML for virtio backend 

This is in response to:

   https://bugzilla.redhat.com/show_bug.cgi?id=629662

Explanation

qemu's virtio-net-pci driver allows setting the algorithm used for tx
packets to either "bh" or "timer". This is done by adding ",tx=bh" or
",tx=timer" to the "-device virtio-net-pci" commandline option.

'bh' stands for 'bottom half'; when this is set, packet tx is all done
in an iothread in the bottom half of the driver. (In libvirt, this
option is called the more descriptive "iothread".)

'timer' means that tx work is done in qemu, and if there is more tx
data than can be sent at the present time, a timer is set before qemu
moves on to do other things; when the timer fires, another attempt is
made to send more data. (libvirt retains the name "timer" for this
option.)

The resulting difference, according to the qemu developer who added
the option is:

    bh makes tx more asynchronous and reduces latency, but potentially
    causes more processor bandwidth contention since the cpu doing the
    tx isn't necessarily the cpu where the guest generated the
    packets.

Solution

This patch provides a libvirt domain xml knob to change the option on
the qemu commandline, by adding a new attribute "txmode" to the
<driver> element that can be placed inside any <interface> element in
a domain definition. It's use would be something like this:

    <interface ...>
      ...
      <model type='virtio'/>
      <driver txmode='iothread'/>
      ...
    </interface>

I chose to put this setting as an attribute to <driver> rather than as
a sub-element to <tune> because it is specific to the virtio-net
driver, not something that is generally usable by all network drivers.
(note that this is the same placement as the "driver name=..."
attribute used to choose kernel vs. userland backend for the
virtio-net driver.)

Actually adding the tx=xxx option to the qemu commandline is only done
if the version of qemu being used advertises it in the output of

    qemu -device virtio-net-pci,?

If a particular txmode is requested in the XML, and the option isn't
listed in that help output, an UNSUPPORTED_CONFIG error is logged, and
the domain fails to start.
This commit is contained in:
Laine Stump 2011-02-03 15:20:01 -05:00
parent b670a41206
commit e9bd5c0e24
14 changed files with 180 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

50
docs/formatdomain.html.in
View File

@ -1378,6 +1378,56 @@ qemu-kvm -net nic,model=? /dev/null
ne2k_isa i82551 i82557b i82559er ne2k_pci pcnet rtl8139 e1000 virtio
</p>
<h5><a name="elementsDriverBackendOptions">Setting NIC driver-specific options</a></h5>
<pre>
...
&lt;devices&gt;
&lt;interface type='network'&gt;
&lt;source network='default'/&gt;
&lt;target dev='vnet1'/&gt;
&lt;model type='virtio'/&gt;
<b>&lt;driver txmode='iothread'/&gt;</b>
&lt;/interface&gt;
&lt;/devices&gt;
...</pre>
<p>
Some NICs may have tunable driver-specific options. These are
set as attributes of the <code>driver</code> sub-element of the
interface definition. Currently the following attributes are
available for the <code>"virtio"</code> NIC driver:
</p>
<dl>
<dt><code>txmode</code></dt>
<dd>
The <code>txmode</code> attribute specifies how to handle
transmission of packets when the transmit buffer is full. The
value can be either 'iothread' or 'timer'.
<span class="since">Since 0.8.8 (QEMU and KVM only)</span><br><br>
If set to 'iothread', packet tx is all done in an iothread in
the bottom half of the driver (this option translates into
adding "tx=bh" to the qemu commandline -device virtio-net-pci
option).<br><br>
If set to 'timer', tx work is done in qemu, and if there is
more tx data than can be sent at the present time, a timer is
set before qemu moves on to do other things; when the timer
fires, another attempt is made to send more data.<br><br>
The resulting difference, according to the qemu developer who
added the option is: "bh makes tx more asynchronous and reduces
latency, but potentially causes more processor bandwidth
contention since the cpu doing the tx isn't necessarily the
cpu where the guest generated the packets."<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>
<h5><a name="elementsNICSTargetOverride">Overriding the target element</a></h5>
<pre>

8
docs/schemas/domain.rng
View File

@ -1042,6 +1042,14 @@
</choice>
</attribute>
</optional>
<optional>
<attribute name="txmode">
<choice>
<value>iothread</value>
<value>timer</value>
</choice>
</attribute>
</optional>
<empty/>
</element>
</optional>

26
src/conf/domain_conf.c
View File

@ -198,6 +198,11 @@ VIR_ENUM_IMPL(virDomainNetBackend, VIR_DOMAIN_NET_BACKEND_TYPE_LAST,
"qemu",
"vhost")
VIR_ENUM_IMPL(virDomainNetVirtioTxMode, VIR_DOMAIN_NET_VIRTIO_TX_MODE_LAST,
"default",
"iothread",
"timer")
VIR_ENUM_IMPL(virDomainChrChannelTarget,
VIR_DOMAIN_CHR_CHANNEL_TARGET_TYPE_LAST,
"guestfwd",
@ -2477,6 +2482,7 @@ virDomainNetDefParseXML(virCapsPtr caps,
char *port = NULL;
char *model = NULL;
char *backend = NULL;
char *txmode = NULL;
char *filter = NULL;
char *internal = NULL;
char *devaddr = NULL;
@ -2565,6 +2571,7 @@ virDomainNetDefParseXML(virCapsPtr caps,
model = virXMLPropString(cur, "type");
} else if (xmlStrEqual (cur->name, BAD_CAST "driver")) {
backend = virXMLPropString(cur, "name");
txmode = virXMLPropString(cur, "txmode");
} else if (xmlStrEqual (cur->name, BAD_CAST "filterref")) {
filter = virXMLPropString(cur, "filter");
VIR_FREE(filterparams);
@ -2769,6 +2776,18 @@ virDomainNetDefParseXML(virCapsPtr caps,
}
def->driver.virtio.name = name;
}
if (txmode != NULL) {
int m;
if (((m = virDomainNetVirtioTxModeTypeFromString(txmode)) < 0) ||
(m == VIR_DOMAIN_NET_VIRTIO_TX_MODE_DEFAULT)) {
virDomainReportError(VIR_ERR_INTERNAL_ERROR,
_("Unknown interface <driver txmode='%s'> "
"has been specified"),
txmode);
goto error;
}
def->driver.virtio.txmode = m;
}
}
if (filter != NULL) {
@ -2808,6 +2827,7 @@ cleanup:
VIR_FREE(bridge);
VIR_FREE(model);
VIR_FREE(backend);
VIR_FREE(txmode);
VIR_FREE(filter);
VIR_FREE(type);
VIR_FREE(internal);
@ -6813,12 +6833,16 @@ virDomainNetDefFormat(virBufferPtr buf,
virBufferEscapeString(buf, " <model type='%s'/>\n",
def->model);
if (STREQ(def->model, "virtio") &&
def->driver.virtio.name) {
(def->driver.virtio.name || def->driver.virtio.txmode)) {
virBufferAddLit(buf, " <driver");
if (def->driver.virtio.name) {
virBufferVSprintf(buf, " name='%s'",
virDomainNetBackendTypeToString(def->driver.virtio.name));
}
if (def->driver.virtio.txmode) {
virBufferVSprintf(buf, " txmode='%s'",
virDomainNetVirtioTxModeTypeToString(def->driver.virtio.txmode));
}
virBufferAddLit(buf, "/>\n");
}
}

11
src/conf/domain_conf.h
View File

@ -321,6 +321,15 @@ enum virDomainNetBackendType {
VIR_DOMAIN_NET_BACKEND_TYPE_LAST,
};
/* the TX algorithm used for virtio interfaces */
enum virDomainNetVirtioTxModeType {
VIR_DOMAIN_NET_VIRTIO_TX_MODE_DEFAULT, /* default for this version of qemu */
VIR_DOMAIN_NET_VIRTIO_TX_MODE_IOTHREAD,
VIR_DOMAIN_NET_VIRTIO_TX_MODE_TIMER,
VIR_DOMAIN_NET_VIRTIO_TX_MODE_LAST,
};
/* the mode type for macvtap devices */
enum virDomainNetdevMacvtapType {
VIR_DOMAIN_NETDEV_MACVTAP_MODE_VEPA,
@ -341,6 +350,7 @@ struct _virDomainNetDef {
union {
struct {
enum virDomainNetBackendType name; /* which driver backend to use */
enum virDomainNetVirtioTxModeType txmode;
} virtio;
} driver;
union {
@ -1371,6 +1381,7 @@ VIR_ENUM_DECL(virDomainFS)
VIR_ENUM_DECL(virDomainFSAccessMode)
VIR_ENUM_DECL(virDomainNet)
VIR_ENUM_DECL(virDomainNetBackend)
VIR_ENUM_DECL(virDomainNetVirtioTxMode)
VIR_ENUM_DECL(virDomainChrDevice)
VIR_ENUM_DECL(virDomainChrChannelTarget)
VIR_ENUM_DECL(virDomainChrConsoleTarget)

3
src/qemu/qemu_capabilities.c
View File

@ -1074,6 +1074,7 @@ qemuCapsExtractDeviceStr(const char *qemu,
"-device", "?",
"-device", "pci-assign,?",
"-device", "virtio-blk-pci,?",
"-device", "virtio-net-pci,?",
NULL);
virCommandAddEnvPassCommon(cmd);
/* qemu -help goes to stdout, but qemu -device ? goes to stderr. */
@ -1115,6 +1116,8 @@ qemuCapsParseDeviceStr(const char *str, unsigned long long *flags)
if (strstr(str, "pci-assign.bootindex"))
*flags |= QEMUD_CMD_FLAG_PCI_BOOTINDEX;
}
if (strstr(str, "virtio-net-pci.tx="))
*flags |= QEMUD_CMD_FLAG_VIRTIO_TX_ALG;
return 0;
}

1
src/qemu/qemu_capabilities.h
View File

@ -92,6 +92,7 @@ enum qemuCapsFlags {
QEMUD_CMD_FLAG_CCID_PASSTHRU = (1LL << 55), /* -device ccid-card-passthru */
QEMUD_CMD_FLAG_CHARDEV_SPICEVMC = (1LL << 56), /* newer -chardev spicevmc */
QEMUD_CMD_FLAG_DEVICE_SPICEVMC = (1LL << 57), /* older -device spicevmc*/
QEMUD_CMD_FLAG_VIRTIO_TX_ALG = (1LL << 58), /* -device virtio-net-pci,tx=string */
};
virCapsPtr qemuCapsInit(virCapsPtr old_caps);

27
src/qemu/qemu_command.c
View File

@ -1606,16 +1606,43 @@ qemuBuildNicDevStr(virDomainNetDefPtr net,
{
virBuffer buf = VIR_BUFFER_INITIALIZER;
const char *nic;
bool usingVirtio = false;
if (!net->model) {
nic = "rtl8139";
} else if (STREQ(net->model, "virtio")) {
nic = "virtio-net-pci";
usingVirtio = true;
} else {
nic = net->model;
}
virBufferAdd(&buf, nic, strlen(nic));
if (usingVirtio && net->driver.virtio.txmode) {
if (qemuCmdFlags & QEMUD_CMD_FLAG_VIRTIO_TX_ALG) {
virBufferAddLit(&buf, ",tx=");
switch (net->driver.virtio.txmode) {
case VIR_DOMAIN_NET_VIRTIO_TX_MODE_IOTHREAD:
virBufferAddLit(&buf, "bh");
break;
case VIR_DOMAIN_NET_VIRTIO_TX_MODE_TIMER:
virBufferAddLit(&buf, "timer");
break;
default:
/* this should never happen, if it does, we need
* to add another case to this switch.
*/
qemuReportError(VIR_ERR_INTERNAL_ERROR, "%s",
_("unrecognized virtio-net-pci 'tx' option"));
goto error;
}
} else {
qemuReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
_("virtio-net-pci 'tx' option not supported in this QEMU binary"));
goto error;
}
}
if (vlan == -1)
virBufferVSprintf(&buf, ",netdev=host%s", net->info.alias);
else

25
tests/qemuhelpdata/qemu-kvm-0.12.1.2-rhel61-device
View File

@ -72,3 +72,28 @@ virtio-blk-pci.ioeventfd=on/off
virtio-blk-pci.vectors=uint32
virtio-blk-pci.indirect_desc=on/off
virtio-blk-pci.scsi=on/off
virtio-net-pci.vectors=uint32
virtio-net-pci.indirect_desc=on/off
virtio-net-pci.csum=on/off
virtio-net-pci.guest_csum=on/off
virtio-net-pci.gso=on/off
virtio-net-pci.guest_tso4=on/off
virtio-net-pci.guest_tso6=on/off
virtio-net-pci.guest_ecn=on/off
virtio-net-pci.guest_ufo=on/off
virtio-net-pci.host_tso4=on/off
virtio-net-pci.host_tso6=on/off
virtio-net-pci.host_ecn=on/off
virtio-net-pci.host_ufo=on/off
virtio-net-pci.mrg_rxbuf=on/off
virtio-net-pci.status=on/off
virtio-net-pci.ctrl_vq=on/off
virtio-net-pci.ctrl_rx=on/off
virtio-net-pci.ctrl_vlan=on/off
virtio-net-pci.ctrl_rx_extra=on/off
virtio-net-pci.mac=macaddr
virtio-net-pci.vlan=vlan
virtio-net-pci.netdev=netdev
virtio-net-pci.x-txtimer=uint32
virtio-net-pci.x-txburst=int32
virtio-net-pci.tx=string

22
tests/qemuhelpdata/qemu-kvm-0.13.0-device
View File

@ -68,3 +68,25 @@ name "pci-assign", bus PCI, desc "pass through host pci devices to the guest"
pci-assign.host=pci-hostaddr
pci-assign.iommu=uint32
pci-assign.configfd=string
virtio-net-pci.vectors=uint32
virtio-net-pci.indirect_desc=on/off
virtio-net-pci.csum=on/off
virtio-net-pci.guest_csum=on/off
virtio-net-pci.gso=on/off
virtio-net-pci.guest_tso4=on/off
virtio-net-pci.guest_tso6=on/off
virtio-net-pci.guest_ecn=on/off
virtio-net-pci.guest_ufo=on/off
virtio-net-pci.host_tso4=on/off
virtio-net-pci.host_tso6=on/off
virtio-net-pci.host_ecn=on/off
virtio-net-pci.host_ufo=on/off
virtio-net-pci.mrg_rxbuf=on/off
virtio-net-pci.status=on/off
virtio-net-pci.ctrl_vq=on/off
virtio-net-pci.ctrl_rx=on/off
virtio-net-pci.ctrl_vlan=on/off
virtio-net-pci.ctrl_rx_extra=on/off
virtio-net-pci.mac=macaddr
virtio-net-pci.vlan=vlan
virtio-net-pci.netdev=netdev

3
tests/qemuhelptest.c
View File

@ -480,7 +480,8 @@ mymain(int argc, char **argv)
QEMUD_CMD_FLAG_HDA_DUPLEX |
QEMUD_CMD_FLAG_DRIVE_AIO |
QEMUD_CMD_FLAG_CCID_PASSTHRU |
QEMUD_CMD_FLAG_CHARDEV_SPICEVMC,
QEMUD_CMD_FLAG_CHARDEV_SPICEVMC |
QEMUD_CMD_FLAG_VIRTIO_TX_ALG,
12001, 1, 0);
return ret == 0 ? EXIT_SUCCESS : EXIT_FAILURE;

2
tests/qemuxml2argvdata/qemuxml2argv-net-virtio-device.args
View File

@ -1,6 +1,6 @@
LC_ALL=C PATH=/bin HOME=/home/test USER=test LOGNAME=test /usr/bin/qemu -S -M \
pc -m 214 -smp 1 -nographic -nodefconfig -nodefaults -monitor \
unix:/tmp/test-monitor,server,nowait -no-acpi -boot c -hda \
/dev/HostVG/QEMUGuest1 -device virtio-net-pci,vlan=0,id=net0,\
/dev/HostVG/QEMUGuest1 -device virtio-net-pci,tx=bh,vlan=0,id=net0,\
mac=00:11:22:33:44:55,bus=pci.0,addr=0x2 -net user,vlan=0,name=hostnet0 -usb \
-device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x3

3
tests/qemuxml2argvdata/qemuxml2argv-net-virtio-device.xml
View File

@ -17,10 +17,13 @@
<disk type='block' device='disk'>
<source dev='/dev/HostVG/QEMUGuest1'/>
<target dev='hda' bus='ide'/>
<address type='drive' controller='0' bus='0' unit='0'/>
</disk>
<controller type='ide' index='0'/>
<interface type='user'>
<mac address='00:11:22:33:44:55'/>
<model type='virtio'/>
<driver txmode='iothread'/>
</interface>
<memballoon model='virtio'/>
</devices>

2
tests/qemuxml2argvtest.c
View File

@ -365,7 +365,7 @@ mymain(int argc, char **argv)
DO_TEST("net-user", 0, false);
DO_TEST("net-virtio", 0, false);
DO_TEST("net-virtio-device", QEMUD_CMD_FLAG_DEVICE |
QEMUD_CMD_FLAG_NODEFCONFIG, false);
QEMUD_CMD_FLAG_NODEFCONFIG | QEMUD_CMD_FLAG_VIRTIO_TX_ALG, false);
DO_TEST("net-virtio-netdev", QEMUD_CMD_FLAG_DEVICE |
QEMUD_CMD_FLAG_NETDEV | QEMUD_CMD_FLAG_NODEFCONFIG, false);
DO_TEST("net-eth", 0, false);

1
tests/qemuxml2xmltest.c
View File

@ -159,6 +159,7 @@ mymain(int argc, char **argv)
DO_TEST("misc-no-reboot");
DO_TEST("net-user");
DO_TEST("net-virtio");
DO_TEST("net-virtio-device");
DO_TEST("net-eth");
DO_TEST("net-eth-ifname");
DO_TEST("sound");