3 p.m.
qemu's virtio-net-pci driver allows setting the algorithm used for tx
packets to either "bh" or "timer". I don't know exactly how these
algorithms differ, but someone has requested the ability to choose
between them in libvirt's domain XML. See:
https://bugzilla.redhat.com/show_bug.cgi?id=629662
This patch provides that knob, by adding a new attribute "tx_alg" 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 tx_alg='bh'/>
...
</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.) This is a bit troublesome to me, because I can see
lots of new virtio options that could potentially be requested (just
run "qemu-kvm -device virtio-net-pci,?" on a qemu that's version
0.13.0 or newer, and compare that output to potential tunable items in
"-device e1000,?" or "-net tap,..."), so the attribute list could
potentially get quite long (which is something I was concerned about
when I first added the option to select kernel vs. userland backend,
but didn't realize just how many virtio-specific options there were).
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 the option isn't listed there, the config item is ignored (should
it instead generate a warning log? error out and prevent the domain
from starting?)
---
src/conf/domain_conf.c | 26 +++++++++++++++++++++++++-
src/conf/domain_conf.h | 11 +++++++++++
src/libvirt_private.syms | 1 +
src/qemu/qemu_capabilities.c | 3 +++
src/qemu/qemu_capabilities.h | 1 +
src/qemu/qemu_command.c | 13 +++++++++++++
6 files changed, 54 insertions(+), 1 deletions(-)
diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
index 84b866b..8f0f057 100644
--- a/src/conf/domain_conf.c
+++ b/src/conf/domain_conf.c
@@ -198,6 +198,11 @@ VIR_ENUM_IMPL(virDomainNetBackend, VIR_DOMAIN_NET_BACKEND_TYPE_LAST,
"qemu",
"vhost")
+VIR_ENUM_IMPL(virDomainNetVirtioTxAlg, VIR_DOMAIN_NET_BACKEND_TYPE_LAST,
+ "default",
+ "bh",
+ "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 *tx_alg = 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");
+ tx_alg = virXMLPropString(cur, "tx_alg");
} 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 (tx_alg != NULL) {
+ int alg;
+ if (((alg = virDomainNetVirtioTxAlgTypeFromString(tx_alg)) < 0) ||
+ (alg == VIR_DOMAIN_NET_VIRTIO_TX_ALG_DEFAULT)) {
+ virDomainReportError(VIR_ERR_INTERNAL_ERROR,
+ _("Unknown interface <driver
tx_alg='%s'> "
+ "has been specified"),
+ tx_alg);
+ goto error;
+ }
+ def->driver.virtio.tx_alg = alg;
+ }
}
if (filter != NULL) {
@@ -2808,6 +2827,7 @@ cleanup:
VIR_FREE(bridge);
VIR_FREE(model);
VIR_FREE(backend);
+ VIR_FREE(tx_alg);
VIR_FREE(filter);
VIR_FREE(type);
VIR_FREE(internal);
@@ -6808,12 +6828,16 @@ 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.tx_alg)) {
virBufferAddLit(buf, " <driver");
if (def->driver.virtio.name) {
virBufferVSprintf(buf, " name='%s'",
virDomainNetBackendTypeToString(def->driver.virtio.name));
}
+ if (def->driver.virtio.tx_alg) {
+ virBufferVSprintf(buf, " tx_alg='%s'",
+
virDomainNetVirtioTxAlgTypeToString(def->driver.virtio.tx_alg));
+ }
virBufferAddLit(buf, "/>\n");
}
}
diff --git a/src/conf/domain_conf.h b/src/conf/domain_conf.h
index 44d0a4b..b3a02f4 100644
--- a/src/conf/domain_conf.h
+++ b/src/conf/domain_conf.h
@@ -321,6 +321,15 @@ enum virDomainNetBackendType {
VIR_DOMAIN_NET_BACKEND_TYPE_LAST,
};
+/* the TX algorithm used for virtio interfaces */
+enum virDomainNetVirtioTxAlgType {
+ VIR_DOMAIN_NET_VIRTIO_TX_ALG_DEFAULT, /* default for this version of qemu */
+ VIR_DOMAIN_NET_VIRTIO_TX_ALG_BH,
+ VIR_DOMAIN_NET_VIRTIO_TX_ALG_TIMER,
+
+ VIR_DOMAIN_NET_VIRTIO_TX_ALG_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 virDomainNetVirtioTxAlgType tx_alg;
} virtio;
} driver;
union {
@@ -1367,6 +1377,7 @@ VIR_ENUM_DECL(virDomainFS)
VIR_ENUM_DECL(virDomainFSAccessMode)
VIR_ENUM_DECL(virDomainNet)
VIR_ENUM_DECL(virDomainNetBackend)
+VIR_ENUM_DECL(virDomainNetVirtioTxAlg)
VIR_ENUM_DECL(virDomainChrDevice)
VIR_ENUM_DECL(virDomainChrChannelTarget)
VIR_ENUM_DECL(virDomainChrConsoleTarget)
diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
index 88e270c..dd44749 100644
--- a/src/libvirt_private.syms
+++ b/src/libvirt_private.syms
@@ -268,6 +268,7 @@ virDomainMemballoonModelTypeFromString;
virDomainMemballoonModelTypeToString;
virDomainNetDefFree;
virDomainNetTypeToString;
+virDomainNetVirtioTxAlgTypeToString;
virDomainObjAssignDef;
virDomainObjSetDefTransient;
virDomainObjGetPersistentDef;
diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c
index 0e1f79c..935c669 100644
--- a/src/qemu/qemu_capabilities.c
+++ b/src/qemu/qemu_capabilities.c
@@ -1063,6 +1063,7 @@ 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. */
@@ -1104,6 +1105,8 @@ 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;
}
diff --git a/src/qemu/qemu_capabilities.h b/src/qemu/qemu_capabilities.h
index dd39b3b..c29d914 100644
--- a/src/qemu/qemu_capabilities.h
+++ b/src/qemu/qemu_capabilities.h
@@ -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);
diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
index 1b213da..1d6f20c 100644
--- a/src/qemu/qemu_command.c
+++ b/src/qemu/qemu_command.c
@@ -1577,16 +1577,29 @@ 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.tx_alg) {
+ if (qemuCmdFlags & QEMUD_CMD_FLAG_VIRTIO_TX_ALG) {
+ virBufferVSprintf(&buf, ",tx=%s",
+
virDomainNetVirtioTxAlgTypeToString(net->driver.virtio.tx_alg));
+ } else {
+ /* What should we do if the option isn't available? log a
+ * warning? prevent the domain from starting? Ignore it?
+ * Right now we're ignoring it.
+ */
+ }
+ }
if (vlan == -1)
virBufferVSprintf(&buf, ",netdev=host%s", net->info.alias);
else
--
1.7.3.4