| Message ID | 1518542328-25741-3-git-send-email-mihajlov@linux.vnet.ibm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tue, 13 Feb 2018 18:18:47 +0100 Viktor Mihajlovski <mihajlov@linux.vnet.ibm.com> wrote: > From: Luiz Capitulino <lcapitulino@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", "arch" > and "halted" I'd suggest updating this description, as "halted" is now gone completely... what about: o Drop the "halted" field, even if the halted state is maintained by QEMU. It had unclear semantics anyway. o Drop irrelevant fields such as "current", "pc", or "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> > --- > cpus.c | 38 ++++++++++++++++++++++++++++ > hmp-commands-info.hx | 14 +++++++++++ > hmp.c | 14 +++++++++++ > hmp.h | 1 + > qapi-schema.json | 70 ++++++++++++++++++++++++++++++++++++++++++++++++++++ > 5 files changed, 137 insertions(+) Otherwise, looks good to me. Reviewed-by: Cornelia Huck <cohuck@redhat.com>
On 02/13/2018 11:18 AM, Viktor Mihajlovski wrote: > From: Luiz Capitulino <lcapitulino@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", "arch" > and "halted" > Others have pointed out the commit message inconsistencies; I'm focusing on the QMP. > +++ 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 s/an small interruption/a small interruption to/ > +# 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' } } Comparing against the existing CpuInfo: if I'm not mistaken, you've renamed: CPU -> cpu-index qom_path -> qom-path thread_id -> thread-id and kept props unchanged. If we REALLY cared about reducing duplication, we can do: { 'struct': 'CpuInfoFast', 'data': { 'CPU': 'int', 'qom_path': 'str', 'thread_id': 'int', '*props': 'CpuInstanceProperties' } } { 'struct': 'CpuInfoBase', 'base': 'CpuInfoFast', 'data': { 'current': 'bool', 'halted': 'bool', 'arch': 'CpuInfoArch' } } { 'union': 'CpuInfo', 'base': 'CpuInfoBase', 'discriminator': 'arch', 'data': { ... } } but I'm not yet convinced whether we need that. If we're going to deprecate the old command, having the new command use modern spelling is a nice change, even though it costs some duplication in the qapi file; where sharing code may save qapi costs in the short run, but will burden us with poor naming down the road even when we delete the slow command. > + > +## > +# @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 > +{ 'command': 'query-cpus-fast', 'returns': [ 'CpuInfoFast' ] } > + > +## > # @IOThreadInfo: > # > # Information about an iothread > I didn't inspect the code, so similar to 1/3, once you fix the grammar nit and commit message, Acked-by: Eric Blake <eblake@redhat.com>
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..0bd3b3a 100644 --- a/hmp.c +++ b/hmp.c @@ -410,6 +410,20 @@ 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; + + head = qmp_query_cpus_fast(NULL); + + for (cpu = head; cpu; cpu = cpu->next) { + monitor_printf(mon, " CPU #%" PRId64 ":", cpu->value->cpu_index); + monitor_printf(mon, " thread-id=%" PRId64 "\n", cpu->value->thread_id); + } + + 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); diff --git a/qapi-schema.json b/qapi-schema.json index 94d560e..dc07729 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