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util: Add write-only "node-affinity" property for ThreadContext

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Let's make it easier to pin threads created via a ThreadContext to
all host CPUs currently belonging to a given set of host NUMA nodes --
which is the common case.

"node-affinity" is simply a shortcut for setting "cpu-affinity" manually
to the list of host CPUs belonging to the set of host nodes. This property
can only be written.

A simple QEMU example to set the CPU affinity to host node 1 on a system
with two nodes, 24 CPUs each, whereby odd-numbered host CPUs belong to
host node 1:
    qemu-system-x86_64 -S \
      -object thread-context,id=tc1,node-affinity=1

And we can query the cpu-affinity via HMP/QMP:
    (qemu) qom-get tc1 cpu-affinity
    [
        1,
        3,
        5,
        7,
        9,
        11,
        13,
        15,
        17,
        19,
        21,
        23,
        25,
        27,
        29,
        31,
        33,
        35,
        37,
        39,
        41,
        43,
        45,
        47
    ]

We cannot query the node-affinity:
    (qemu) qom-get tc1 node-affinity
    Error: Insufficient permission to perform this operation

But note that due to dynamic library loading this example will not work
before we actually make use of thread_context_create_thread() in QEMU
code, because the type will otherwise not get registered. We'll wire
this up next to make it work.

Note that if the host CPUs for a host node change due do CPU hot(un)plug
CPU onlining/offlining (i.e., lscpu output changes) after the ThreadContext
was started, the CPU affinity will not get updated.

Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Acked-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20221014134720.168738-5-david@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
This commit is contained in:
David Hildenbrand 2022-10-14 15:47:17 +02:00
parent e2de2c497e
commit 10218ae6d0
3 changed files with 93 additions and 2 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

9
qapi/qom.json
View file

@ -839,10 +839,17 @@
# threads created in the thread context (default: QEMU main
# thread CPU affinity)
#
# @node-affinity: the list of host node numbers that will be resolved to a
# list of host CPU numbers used as CPU affinity. This is a
# shortcut for specifying the list of host CPU numbers
# belonging to the host nodes manually by setting
# @cpu-affinity. (default: QEMU main thread affinity)
#
# Since: 7.2
##
{ 'struct': 'ThreadContextProperties',
'data': { '*cpu-affinity': ['uint16'] } }
'data': { '*cpu-affinity': ['uint16'],
'*node-affinity': ['uint16'] } }
##

2
util/meson.build
View file

@ -1,5 +1,5 @@
util_ss.add(files('osdep.c', 'cutils.c', 'unicode.c', 'qemu-timer-common.c'))
util_ss.add(files('thread-context.c'))
util_ss.add(files('thread-context.c'), numa)
if not config_host_data.get('CONFIG_ATOMIC64')
util_ss.add(files('atomic64.c'))
endif

84
util/thread-context.c
View file

@ -21,6 +21,10 @@
#include "qemu/module.h"
#include "qemu/bitmap.h"
#ifdef CONFIG_NUMA
#include <numa.h>
#endif
enum {
TC_CMD_NONE = 0,
TC_CMD_STOP,
@ -88,6 +92,11 @@ static void thread_context_set_cpu_affinity(Object *obj, Visitor *v,
int nbits = 0, ret;
Error *err = NULL;
if (tc->init_cpu_bitmap) {
error_setg(errp, "Mixing CPU and node affinity not supported");
return;
}
visit_type_uint16List(v, name, &host_cpus, &err);
if (err) {
error_propagate(errp, err);
@ -159,6 +168,79 @@ static void thread_context_get_cpu_affinity(Object *obj, Visitor *v,
qapi_free_uint16List(host_cpus);
}
static void thread_context_set_node_affinity(Object *obj, Visitor *v,
const char *name, void *opaque,
Error **errp)
{
#ifdef CONFIG_NUMA
const int nbits = numa_num_possible_cpus();
ThreadContext *tc = THREAD_CONTEXT(obj);
uint16List *l, *host_nodes = NULL;
unsigned long *bitmap = NULL;
struct bitmask *tmp_cpus;
Error *err = NULL;
int ret, i;
if (tc->init_cpu_bitmap) {
error_setg(errp, "Mixing CPU and node affinity not supported");
return;
}
visit_type_uint16List(v, name, &host_nodes, &err);
if (err) {
error_propagate(errp, err);
return;
}
if (!host_nodes) {
error_setg(errp, "Node list is empty");
goto out;
}
bitmap = bitmap_new(nbits);
tmp_cpus = numa_allocate_cpumask();
for (l = host_nodes; l; l = l->next) {
numa_bitmask_clearall(tmp_cpus);
ret = numa_node_to_cpus(l->value, tmp_cpus);
if (ret) {
/* We ignore any errors, such as impossible nodes. */
continue;
}
for (i = 0; i < nbits; i++) {
if (numa_bitmask_isbitset(tmp_cpus, i)) {
set_bit(i, bitmap);
}
}
}
numa_free_cpumask(tmp_cpus);
if (bitmap_empty(bitmap, nbits)) {
error_setg(errp, "The nodes select no CPUs");
goto out;
}
if (tc->thread_id != -1) {
/*
* Note: we won't be adjusting the affinity of any thread that is still
* around for now, but only the affinity of the context thread.
*/
ret = qemu_thread_set_affinity(&tc->thread, bitmap, nbits);
if (ret) {
error_setg(errp, "Setting CPU affinity failed: %s", strerror(ret));
}
} else {
tc->init_cpu_bitmap = bitmap;
bitmap = NULL;
tc->init_cpu_nbits = nbits;
}
out:
g_free(bitmap);
qapi_free_uint16List(host_nodes);
#else
error_setg(errp, "NUMA node affinity is not supported by this QEMU");
#endif
}
static void thread_context_get_thread_id(Object *obj, Visitor *v,
const char *name, void *opaque,
Error **errp)
@ -208,6 +290,8 @@ static void thread_context_class_init(ObjectClass *oc, void *data)
object_class_property_add(oc, "cpu-affinity", "int",
thread_context_get_cpu_affinity,
thread_context_set_cpu_affinity, NULL, NULL);
object_class_property_add(oc, "node-affinity", "int", NULL,
thread_context_set_node_affinity, NULL, NULL);
}
static void thread_context_instance_init(Object *obj)