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authorLuiz Capitulino <lcapitulino@redhat.com>2018-02-16 17:08:38 +0100
committerCornelia Huck <cohuck@redhat.com>2018-02-26 12:55:26 +0100
commitce74ee3dea6273a7a6aebc157f39cffd3e388097 (patch)
treeddf9a831cb283c30072532b3c4391cb1ef72ce44
parent9d0306dfdfb7e7fd8d5fbe45973566d1a8ea592d (diff)
downloadqemu-arm-ce74ee3dea6273a7a6aebc157f39cffd3e388097.tar.gz
qmp: add query-cpus-fast
The query-cpus command has an extremely serious side effect: it always interrupts all running vCPUs so that they can run ioctl calls. This can cause a huge performance degradation for some workloads. And most of the information retrieved by the ioctl calls are not even used by query-cpus. This commit introduces a replacement for query-cpus called query-cpus-fast, which has the following features: o Never interrupt vCPUs threads. query-cpus-fast only returns vCPU information maintained by QEMU itself, which should be sufficient for most management software needs o Drop "halted" field as it can not be retrieved in a fast way on most architectures o Drop irrelevant fields such as "current", "pc" and "arch" o Rename some fields for better clarification & proper naming standard Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com> Signed-off-by: Viktor Mihajlovski <mihajlov@linux.vnet.ibm.com> Message-Id: <1518797321-28356-3-git-send-email-mihajlov@linux.vnet.ibm.com> Reviewed-by: Cornelia Huck <cohuck@redhat.com> Reviewed-by: Eric Blake <eblake@redhat.com> Signed-off-by: Cornelia Huck <cohuck@redhat.com>
-rw-r--r--cpus.c38
-rw-r--r--qapi-schema.json70
2 files changed, 108 insertions, 0 deletions
diff --git a/cpus.c b/cpus.c
index 6006931d3a..6df6660ccf 100644
--- a/cpus.c
+++ b/cpus.c
@@ -2156,6 +2156,44 @@ CpuInfoList *qmp_query_cpus(Error **errp)
return head;
}
+/*
+ * fast means: we NEVER interrupt vCPU threads to retrieve
+ * information from KVM.
+ */
+CpuInfoFastList *qmp_query_cpus_fast(Error **errp)
+{
+ MachineState *ms = MACHINE(qdev_get_machine());
+ MachineClass *mc = MACHINE_GET_CLASS(ms);
+ CpuInfoFastList *head = NULL, *cur_item = NULL;
+ CPUState *cpu;
+
+ CPU_FOREACH(cpu) {
+ CpuInfoFastList *info = g_malloc0(sizeof(*info));
+ info->value = g_malloc0(sizeof(*info->value));
+
+ info->value->cpu_index = cpu->cpu_index;
+ info->value->qom_path = object_get_canonical_path(OBJECT(cpu));
+ info->value->thread_id = cpu->thread_id;
+
+ info->value->has_props = !!mc->cpu_index_to_instance_props;
+ if (info->value->has_props) {
+ CpuInstanceProperties *props;
+ props = g_malloc0(sizeof(*props));
+ *props = mc->cpu_index_to_instance_props(ms, cpu->cpu_index);
+ info->value->props = props;
+ }
+
+ if (!cur_item) {
+ head = cur_item = info;
+ } else {
+ cur_item->next = info;
+ cur_item = info;
+ }
+ }
+
+ return head;
+}
+
void qmp_memsave(int64_t addr, int64_t size, const char *filename,
bool has_cpu, int64_t cpu_index, Error **errp)
{
diff --git a/qapi-schema.json b/qapi-schema.json
index 94d560ed13..815f072876 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -552,6 +552,12 @@
#
# Returns a list of information about each virtual CPU.
#
+# This command causes vCPU threads to exit to userspace, which causes
+# a small interruption to guest CPU execution. This will have a negative
+# impact on realtime guests and other latency sensitive guest workloads.
+# It is recommended to use @query-cpus-fast instead of this command to
+# avoid the vCPU interruption.
+#
# Returns: a list of @CpuInfo for each virtual CPU
#
# Since: 0.14.0
@@ -585,6 +591,70 @@
{ 'command': 'query-cpus', 'returns': ['CpuInfo'] }
##
+# @CpuInfoFast:
+#
+# Information about a virtual CPU
+#
+# @cpu-index: index of the virtual CPU
+#
+# @qom-path: path to the CPU object in the QOM tree
+#
+# @thread-id: ID of the underlying host thread
+#
+# @props: properties describing to which node/socket/core/thread
+# virtual CPU belongs to, provided if supported by board
+#
+# Since: 2.12
+#
+##
+{ 'struct': 'CpuInfoFast',
+ 'data': {'cpu-index': 'int', 'qom-path': 'str',
+ 'thread-id': 'int', '*props': 'CpuInstanceProperties' } }
+
+##
+# @query-cpus-fast:
+#
+# Returns information about all virtual CPUs. This command does not
+# incur a performance penalty and should be used in production
+# instead of query-cpus.
+#
+# Returns: list of @CpuInfoFast
+#
+# Notes: The CPU architecture name is not returned by query-cpus-fast.
+# Use query-target to retrieve that information.
+#
+# Since: 2.12
+#
+# Example:
+#
+# -> { "execute": "query-cpus-fast" }
+# <- { "return": [
+# {
+# "thread-id": 25627,
+# "props": {
+# "core-id": 0,
+# "thread-id": 0,
+# "socket-id": 0
+# },
+# "qom-path": "/machine/unattached/device[0]",
+# "cpu-index": 0
+# },
+# {
+# "thread-id": 25628,
+# "props": {
+# "core-id": 0,
+# "thread-id": 0,
+# "socket-id": 1
+# },
+# "qom-path": "/machine/unattached/device[2]",
+# "cpu-index": 1
+# }
+# ]
+# }
+##
+{ 'command': 'query-cpus-fast', 'returns': [ 'CpuInfoFast' ] }
+
+##
# @IOThreadInfo:
#
# Information about an iothread