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hostmem: Allow for specifying a ThreadContext for preallocation

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Let's allow for specifying a thread context via the "prealloc-context"
property. When set, preallcoation threads will be crated via the
thread context -- inheriting the same CPU affinity as the thread
context.

Pinning preallcoation threads to CPUs can heavily increase performance
in NUMA setups, because, preallocation from a CPU close to the target
NUMA node(s) is faster then preallocation from a CPU further remote,
simply because of memory bandwidth for initializing memory with zeroes.
This is especially relevant for very large VMs backed by huge/gigantic
pages, whereby preallocation is mandatory.

Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Message-Id: <20221014134720.168738-7-david@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
This commit is contained in:
David Hildenbrand 2022-10-14 15:47:19 +02:00
parent e04a34e55c
commit e681645862
3 changed files with 15 additions and 3 deletions
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12
backends/hostmem.c
View File

@ -232,8 +232,8 @@ static void host_memory_backend_set_prealloc(Object *obj, bool value,
void *ptr = memory_region_get_ram_ptr(&backend->mr);
uint64_t sz = memory_region_size(&backend->mr);
qemu_prealloc_mem(fd, ptr, sz, backend->prealloc_threads, NULL,
&local_err);
qemu_prealloc_mem(fd, ptr, sz, backend->prealloc_threads,
backend->prealloc_context, &local_err);
if (local_err) {
error_propagate(errp, local_err);
return;
@ -385,7 +385,8 @@ host_memory_backend_memory_complete(UserCreatable *uc, Error **errp)
*/
if (backend->prealloc) {
qemu_prealloc_mem(memory_region_get_fd(&backend->mr), ptr, sz,
backend->prealloc_threads, NULL, &local_err);
backend->prealloc_threads,
backend->prealloc_context, &local_err);
if (local_err) {
goto out;
}
@ -493,6 +494,11 @@ host_memory_backend_class_init(ObjectClass *oc, void *data)
NULL, NULL);
object_class_property_set_description(oc, "prealloc-threads",
"Number of CPU threads to use for prealloc");
object_class_property_add_link(oc, "prealloc-context",
TYPE_THREAD_CONTEXT, offsetof(HostMemoryBackend, prealloc_context),
object_property_allow_set_link, OBJ_PROP_LINK_STRONG);
object_class_property_set_description(oc, "prealloc-context",
"Context to use for creating CPU threads for preallocation");
object_class_property_add(oc, "size", "int",
host_memory_backend_get_size,
host_memory_backend_set_size,

2
include/sysemu/hostmem.h
View File

@ -18,6 +18,7 @@
#include "qom/object.h"
#include "exec/memory.h"
#include "qemu/bitmap.h"
#include "qemu/thread-context.h"
#define TYPE_MEMORY_BACKEND "memory-backend"
OBJECT_DECLARE_TYPE(HostMemoryBackend, HostMemoryBackendClass,
@ -66,6 +67,7 @@ struct HostMemoryBackend {
bool merge, dump, use_canonical_path;
bool prealloc, is_mapped, share, reserve;
uint32_t prealloc_threads;
ThreadContext *prealloc_context;
DECLARE_BITMAP(host_nodes, MAX_NODES + 1);
HostMemPolicy policy;

4
qapi/qom.json
View File

@ -578,6 +578,9 @@
#
# @prealloc-threads: number of CPU threads to use for prealloc (default: 1)
#
# @prealloc-context: thread context to use for creation of preallocation threads
# (default: none) (since 7.2)
#
# @share: if false, the memory is private to QEMU; if true, it is shared
# (default: false)
#
@ -608,6 +611,7 @@
'*policy': 'HostMemPolicy',
'*prealloc': 'bool',
'*prealloc-threads': 'uint32',
'*prealloc-context': 'str',
'*share': 'bool',
'*reserve': 'bool',
'size': 'size',