* Viktor Mihajlovski (mihaj...@linux.vnet.ibm.com) wrote:
> From: Luiz Capitulino <lcapitul...@redhat.com>
>
> 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 Make "halted" field optional: we only return it if the
> halted state is maintained by QEMU. But this also gives
> the option of dropping the field in the future (see below)
>
> o Drop irrelevant fields such as "current", "pc" and "arch"
>
> o Drop field "halted" since it can't be provided fast reliably
> and is too volatile on most architectures to be really useful
>
> o Rename some fields for better clarification & proper naming
> standard
>
> Signed-off-by: Luiz Capitulino <lcapitul...@redhat.com>
> Signed-off-by: Viktor Mihajlovski <mihaj...@linux.vnet.ibm.com>
> ---
> cpus.c | 38 ++++++++++++++++++++++++++++
> hmp-commands-info.hx | 14 +++++++++++
> hmp.c | 21 ++++++++++++++++
> hmp.h | 1 +
> qapi-schema.json | 70
> ++++++++++++++++++++++++++++++++++++++++++++++++++++
> 5 files changed, 144 insertions(+)
>
> diff --git a/cpus.c b/cpus.c
> index 6006931..6df6660 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/hmp-commands-info.hx b/hmp-commands-info.hx
> index ad590a4..16ac602 100644
> --- a/hmp-commands-info.hx
> +++ b/hmp-commands-info.hx
> @@ -160,6 +160,20 @@ Show infos for each CPU.
> ETEXI
>
> {
> + .name = "cpus_fast",
> + .args_type = "",
> + .params = "",
> + .help = "show information for each CPU without interrupting
> them",
> + .cmd = hmp_info_cpus_fast,
> + },
> +
> +STEXI
> +@item info cpus_fast
> +@findex info cpus_fast
> +Show infos for each CPU without performance penalty.
> +ETEXI
> +
> + {
> .name = "history",
> .args_type = "",
> .params = "",
> diff --git a/hmp.c b/hmp.c
> index a6b94b7..598bfe5 100644
> --- a/hmp.c
> +++ b/hmp.c
> @@ -410,6 +410,27 @@ void hmp_info_cpus(Monitor *mon, const QDict *qdict)
> qapi_free_CpuInfoList(cpu_list);
> }
>
> +void hmp_info_cpus_fast(Monitor *mon, const QDict *qdict)
> +{
> + CpuInfoFastList *head, *cpu;
> + TargetInfo *target;
> +
> + target = qmp_query_target(NULL);
> + monitor_printf(mon, "CPU architecture is '%s'\n\n", target->arch);
> + qapi_free_TargetInfo(target);
> +
> + head = qmp_query_cpus_fast(NULL);
> +
> + for (cpu = head; cpu; cpu = cpu->next) {
> + monitor_printf(mon, "CPU%" PRId64 "\n", cpu->value->cpu_index);
> + monitor_printf(mon, " thread-id=%" PRId64 "\n",
> cpu->value->thread_id);
> + monitor_printf(mon, " qom-path=%s\n", cpu->value->qom_path);
> + monitor_printf(mon, "\n");
> + }
> +
> + qapi_free_CpuInfoFastList(head);
> +}
> +
> static void print_block_info(Monitor *mon, BlockInfo *info,
> BlockDeviceInfo *inserted, bool verbose)
> {
> diff --git a/hmp.h b/hmp.h
> index 1143db4..93fb4e4 100644
> --- a/hmp.h
> +++ b/hmp.h
> @@ -29,6 +29,7 @@ void hmp_info_migrate_capabilities(Monitor *mon, const
> QDict *qdict);
> void hmp_info_migrate_parameters(Monitor *mon, const QDict *qdict);
> void hmp_info_migrate_cache_size(Monitor *mon, const QDict *qdict);
> void hmp_info_cpus(Monitor *mon, const QDict *qdict);
> +void hmp_info_cpus_fast(Monitor *mon, const QDict *qdict);
> void hmp_info_block(Monitor *mon, const QDict *qdict);
> void hmp_info_blockstats(Monitor *mon, const QDict *qdict);
> void hmp_info_vnc(Monitor *mon, const QDict *qdict);
For HMP:
Acked-by: Dr. David Alan Gilbert <dgilb...@redhat.com>
> diff --git a/qapi-schema.json b/qapi-schema.json
> index 66e0927..2a614af 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
> +# an small interruption 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
> --
> 1.9.1
>
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
