On 02/07/2018 11:50 AM, Luiz Capitulino wrote:
The query-cpus command has an extremely serious side effect:
it always interrupt all running vCPUs so that they can run
s/interrupt/interrupts/
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 Rename some fields for better clarification & proper naming
standard
The "halted" field is somewhat controversial. On the one hand,
it offers a convenient way to know if a guest CPU is idle or
running. On the other hand, it's a field that can change many
times a second. In fact, the halted state can change even
before query-cpus-fast has returned. This makes one wonder if
this field should be dropped all together. Having the "halted"
field as optional gives a better option for dropping it in
the future, since we can just stop returning it.
Makes sense to me.
Signed-off-by: Luiz Capitulino <lcapitul...@redhat.com>
---
cpus.c | 44 ++++++++++++++++++++++++++++++++
hmp-commands-info.hx | 14 +++++++++++
hmp.c | 24 ++++++++++++++++++
hmp.h | 1 +
qapi-schema.json | 71 ++++++++++++++++++++++++++++++++++++++++++++++++++++
5 files changed, 154 insertions(+)
+++ b/hmp-commands-info.hx
@@ -157,6 +157,20 @@ STEXI
@item info cpus
@findex info cpus
Show infos for each CPU.
Pre-existing, but...
+ETEXI
+
+ {
+ .name = "cpus_fast",
+ .args_type = "",
+ .params = "",
+ .help = "show infos for each CPU without performance penalty",
...copied here. s/infos/information/ in public-facing documentation,
while we're touching it.
+++ b/qapi-schema.json
@@ -558,6 +558,77 @@
##
{ 'command': 'query-cpus', 'returns': ['CpuInfo'] }
+##
+# @CpuInfo2:
Good thing that type names aren't part of our introspection ABI. Would
CpuInfoLite or CpuInfoFast make the code any more legible?
+#
+# Information about a virtual CPU
+#
+# @cpu-index: index of the virtual CPU
+#
+# @halted: true if the virtual CPU is in the halt state. Halt usually refers
+# to a processor specific low power mode. This field is optional,
+# it is only present if the halted state can be retrieved without
+# a performance penalty
Disclaimer is good.
+#
+# @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
+#
+# Notes: @halted is a transient state that changes frequently. By the time the
+# data is sent to the client, the guest may no longer be halted.
+##
+{ 'struct': 'CpuInfo2',
+ 'data': {'cpu-index': 'int', '*halted': 'bool', 'qom-path': 'str',
+ 'thread-id': 'int', '*props': 'CpuInstanceProperties' } }
Looks reasonable.
+
+##
+# @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 @CpuInfo2
+#
+# Notes: The CPU architecture name is not returned by query-cpus-fast.
+# Use query-target to retreive that information.
s/retreive/retrieve/
+##
+{ 'command': 'query-cpus-fast', 'returns': [ 'CpuInfo2' ] }
+
Also, please add some docs to 'query-cpus' pointing to 'query-cpus-fast'.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org