This is in response to a request in: https://bugzilla.redhat.com/show_bug.cgi?id=665293 In short, under heavy load, it's possible for qemu's networking to lock up due to the tap device's default 1MB sndbuf being inadequate. adding "sndbuf=0" to the qemu commandline -netdevice option will alleviate this problem (sndbuf=0 actually sets it to 0xffffffff). Because we must be able to explicitly specify "0" as a value, the standard practice of "0 means not specified" won't work here. Instead, virDomainNetDef also has a sndbuf_specified, which defaults to 0, but is set to 1 if some value was given. The sndbuf value is put inside a <tune> element of each <interface> in the domain. The intent is that further tunable settings will also be placed inside this element. <interface type='network'> ... <tune> <sndbuf>0</sndbuf> ... </tune> </interface> --- Changes from V1: sndbuf_specified is now a bool rather than an int bitfield. sndbuf is now unsigned long. Made possible by eblake's patch adding new virXPath* and virStrToLong_* functions. docs/schemas/domain.rng | 10 ++++++++++ src/conf/domain_conf.c | 29 +++++++++++++++++++++++++++-- src/conf/domain_conf.h | 4 ++++ src/qemu/qemu_command.c | 19 +++++++++++++++++-- 4 files changed, 58 insertions(+), 4 deletions(-) diff --git a/docs/schemas/domain.rng b/docs/schemas/domain.rng index 5e140fb..a79ca6a 100644 --- a/docs/schemas/domain.rng +++ b/docs/schemas/domain.rng @@ -1025,6 +1025,16 @@ <ref name="filterref-node-attributes"/> </element> </optional> + <optional> + <element name="tune"> + <optional> + <!-- size of send buffer for network tap devices --> + <element name="sndbuf"> + <ref name="unsignedInt"/> + </element> + </optional> + </element> + </optional> </interleave> </define> <define name="virtualPortProfile"> diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c index 1cef112..396574e 100644 --- a/src/conf/domain_conf.c +++ b/src/conf/domain_conf.c @@ -2282,6 +2282,7 @@ err_exit: static virDomainNetDefPtr virDomainNetDefParseXML(virCapsPtr caps, xmlNodePtr node, + xmlXPathContextPtr ctxt, int flags ATTRIBUTE_UNUSED) { virDomainNetDefPtr def; xmlNodePtr cur; @@ -2303,12 +2304,15 @@ virDomainNetDefParseXML(virCapsPtr caps, virNWFilterHashTablePtr filterparams = NULL; virVirtualPortProfileParams virtPort; bool virtPortParsed = false; + xmlNodePtr oldnode = ctxt->node; if (VIR_ALLOC(def) < 0) { virReportOOMError(); return NULL; } + ctxt->node = node; + type = virXMLPropString(node, "type"); if (type != NULL) { if ((int)(def->type = virDomainNetTypeFromString(type)) < 0) { @@ -2596,7 +2600,12 @@ virDomainNetDefParseXML(virCapsPtr caps, } } + if (virXPathULong("string(./tune/sndbuf)", ctxt, &def->tune.sndbuf) >= 0) { + def->tune.sndbuf_specified = true; + } + cleanup: + ctxt->node = oldnode; VIR_FREE(macaddr); VIR_FREE(network); VIR_FREE(address); @@ -4306,6 +4315,7 @@ virDomainDeviceDefPtr virDomainDeviceDefParse(virCapsPtr caps, { xmlDocPtr xml; xmlNodePtr node; + xmlXPathContextPtr ctxt = NULL; virDomainDeviceDefPtr dev = NULL; if (!(xml = xmlReadDoc(BAD_CAST xmlStr, "device.xml", NULL, @@ -4322,6 +4332,13 @@ virDomainDeviceDefPtr virDomainDeviceDefParse(virCapsPtr caps, goto error; } + ctxt = xmlXPathNewContext(xml); + if (ctxt == NULL) { + virReportOOMError(); + goto error; + } + ctxt->node = node; + if (VIR_ALLOC(dev) < 0) { virReportOOMError(); goto error; @@ -4337,7 +4354,7 @@ virDomainDeviceDefPtr virDomainDeviceDefParse(virCapsPtr caps, goto error; } else if (xmlStrEqual(node->name, BAD_CAST "interface")) { dev->type = VIR_DOMAIN_DEVICE_NET; - if (!(dev->data.net = virDomainNetDefParseXML(caps, node, flags))) + if (!(dev->data.net = virDomainNetDefParseXML(caps, node, ctxt, flags))) goto error; } else if (xmlStrEqual(node->name, BAD_CAST "input")) { dev->type = VIR_DOMAIN_DEVICE_INPUT; @@ -4375,11 +4392,12 @@ virDomainDeviceDefPtr virDomainDeviceDefParse(virCapsPtr caps, } xmlFreeDoc(xml); - + xmlXPathFreeContext(ctxt); return dev; error: xmlFreeDoc(xml); + xmlXPathFreeContext(ctxt); VIR_FREE(dev); return NULL; } @@ -5050,6 +5068,7 @@ static virDomainDefPtr virDomainDefParseXML(virCapsPtr caps, for (i = 0 ; i < n ; i++) { virDomainNetDefPtr net = virDomainNetDefParseXML(caps, nodes[i], + ctxt, flags); if (!net) goto error; @@ -6318,6 +6337,12 @@ virDomainNetDefFormat(virBufferPtr buf, VIR_FREE(attrs); } + if (def->tune.sndbuf_specified) { + virBufferAddLit(buf, " <tune>\n"); + virBufferVSprintf(buf, " <sndbuf>%lu</sndbuf>\n", def->tune.sndbuf); + virBufferAddLit(buf, " </tune>\n"); + } + if (virDomainDeviceInfoFormat(buf, &def->info, flags) < 0) return -1; diff --git a/src/conf/domain_conf.h b/src/conf/domain_conf.h index a73fd14..1269ed6 100644 --- a/src/conf/domain_conf.h +++ b/src/conf/domain_conf.h @@ -346,6 +346,10 @@ struct _virDomainNetDef { virVirtualPortProfileParams virtPortProfile; } direct; } data; + struct { + bool sndbuf_specified; + unsigned long sndbuf; + } tune; char *ifname; virDomainDeviceInfo info; char *filter; diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c index a3b5ff3..c37fdb2 100644 --- a/src/qemu/qemu_command.c +++ b/src/qemu/qemu_command.c @@ -1584,6 +1584,7 @@ qemuBuildHostNetStr(virDomainNetDefPtr net, const char *tapfd, const char *vhostfd) { + bool is_tap = false; virBuffer buf = VIR_BUFFER_INITIALIZER; switch (net->type) { @@ -1593,6 +1594,7 @@ qemuBuildHostNetStr(virDomainNetDefPtr net, virBufferAddLit(&buf, "tap"); virBufferVSprintf(&buf, "%cfd=%s", type_sep, tapfd); type_sep = ','; + is_tap = true; break; case VIR_DOMAIN_NET_TYPE_ETHERNET: @@ -1606,6 +1608,7 @@ qemuBuildHostNetStr(virDomainNetDefPtr net, net->data.ethernet.script); type_sep = ','; } + is_tap = true; break; case VIR_DOMAIN_NET_TYPE_CLIENT: @@ -1659,8 +1662,11 @@ qemuBuildHostNetStr(virDomainNetDefPtr net, type_sep, net->info.alias); } - if (vhostfd && *vhostfd) { - virBufferVSprintf(&buf, ",vhost=on,vhostfd=%s", vhostfd); + if (is_tap) { + if (vhostfd && *vhostfd) + virBufferVSprintf(&buf, ",vhost=on,vhostfd=%s", vhostfd); + if (net->tune.sndbuf_specified) + virBufferVSprintf(&buf, ",sndbuf=%lu", net->tune.sndbuf); } if (virBufferError(&buf)) { @@ -4661,6 +4667,15 @@ qemuParseCommandLineNet(virCapsPtr caps, } else if (STREQ(keywords[i], "off")) { def->backend = VIR_DOMAIN_NET_BACKEND_TYPE_QEMU; } + } else if (STREQ(keywords[i], "sndbuf") && values[i]) { + if (virStrToLong_ul(values[i], NULL, 10, &def->tune.sndbuf) < 0) { + qemuReportError(VIR_ERR_INTERNAL_ERROR, + _("cannot parse sndbuf size in '%s'"), val); + virDomainNetDefFree(def); + def = NULL; + goto cleanup; + } + def->tune.sndbuf_specified = true; } } -- 1.7.3.4