Re: [PATCH 2/7] qemu_command: Introduce qemuBuildThreadContextProps()

The aim of thread-context object is to set affinity on threads that allocate memory for a memory-backend-* object. For instance: -object '{"qom-type":"thread-context","id":"tc-ram-node0","node-affinity":[3]}' \ -object '{"qom-type":"memory-backend-memfd","id":"ram-node0","hugetlb":true,\ "hugetlbsize":2097152,"share":true,"prealloc":true,"prealloc-threads":8,\ "size":15032385536,"host-nodes":[3],"policy":"preferred",\ "prealloc-context":"tc-ram-node0"}' \ allocates 14GiB worth of memory, backed by 2MiB hugepages from host NUMA node 3, using 8 threads. If it weren't for thread-context these threads wouldn't have any affinity and thus theoretically could be scheduled to run on CPUs of different NUMA node (which is what I saw occasionally). Therefore, whenever we are pinning memory (IOW setting host-nodes attribute), we can generate thread-context object with the same affinity. Signed-off-by: Michal Privoznik <mprivozn(a)redhat.com&gt; --- src/qemu/qemu_command.c | 48 +++++++++++++++++++++++++++++++++++++++++ src/qemu/qemu_command.h | 5 +++++ 2 files changed, 53 insertions(+) diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c index 41b9f7cb52..392b248628 100644 --- a/src/qemu/qemu_command.c +++ b/src/qemu/qemu_command.c @@ -3603,6 +3603,54 @@ qemuBuildMemoryDeviceProps(virQEMUDriverConfig *cfg, } +int +qemuBuildThreadContextProps(virJSONValue **tcProps, + virJSONValue **memProps, + qemuDomainObjPrivate *priv) +{ + g_autoptr(virJSONValue) props = NULL; + virJSONValue *nodemask = NULL; + g_autoptr(virJSONValue) nodemaskCopy = NULL; + g_autofree char *tcAlias = NULL; + const char *memalias = NULL; + + if (tcProps) + *tcProps = NULL; +

+ if (!virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_THREAD_CONTEXT)) + return 0; + + nodemask = virJSONValueObjectGetArray(*memProps, "host-nodes"); + if (!nodemask) + return 0; + + memalias = virJSONValueObjectGetString(*memProps, "id"); + if (!memalias) { + virReportError(VIR_ERR_INTERNAL_ERROR, "%s", + _("memory device alias is not assigned")); + return -1; + } + + tcAlias = g_strdup_printf("tc-%s", memalias); + nodemaskCopy = virJSONValueCopy(nodemask); + + if (virJSONValueObjectAdd(&props, + "s:qom-type", "thread-context", + "s:id", tcAlias, + "a:node-affinity", &nodemaskCopy, + NULL) < 0) + return -1; + + if (virJSONValueObjectAdd(memProps, + "s:prealloc-context", tcAlias, + NULL) < 0) + return -1; + + *tcProps = g_steal_pointer(&props);

+ return 0; +} + + static char * qemuBuildLegacyNicStr(virDomainNetDef *net) { diff --git a/src/qemu/qemu_command.h b/src/qemu/qemu_command.h index 2578367df9..761cc5d865 100644 --- a/src/qemu/qemu_command.h +++ b/src/qemu/qemu_command.h @@ -147,6 +147,11 @@ qemuBuildMemoryDeviceProps(virQEMUDriverConfig *cfg, const virDomainDef *def, const virDomainMemoryDef *mem); +int +qemuBuildThreadContextProps(virJSONValue **tcProps, + virJSONValue **memProps, + qemuDomainObjPrivate *priv); + /* Current, best practice */ virJSONValue * qemuBuildPCIHostdevDevProps(const virDomainDef *def, -- 2.37.4