Re: [PATCH V8 14/15] qapi: examine IOThread attachment status via query-iothreads

[Markus Armbruster <armbru@redhat.com>]

Zhang Chen <zhangckid@gmail.com> writes:

> Extend the 'IOThreadInfo' structure to include attachment metrics.
> This allows users to monitor the associated devices by identify them
> by their QOM paths.

Should we mention block nodes and monitors, too?

>
> New fields added to IOThreadInfo:
>  @holders: IOThreadHolder of the devices currently associated with
>      this iothread.  Users can pre-allocate multiple iothread objects
>      to serve as a persistent thread pool.  When a device is hot-unplugged,
>      it is detached from its iothread, but the iothread remains available,
>      allowing future hot-plugged devices to attach to it.  (Since 11.1)
>
> These fields are also exposed via the Human Monitor Interface (HMP)
> command 'info iothreads' to assist with manual debugging and
> performance tuning.
>
> Signed-off-by: Zhang Chen <zhangckid@gmail.com>
> ---
>  iothread.c         | 22 ++++++++++++++++++++++
>  monitor/hmp-cmds.c | 26 ++++++++++++++++++++++++++
>  qapi/misc.json     | 11 +++++++++++
>  3 files changed, 59 insertions(+)
>
> diff --git a/iothread.c b/iothread.c
> index a85e960e45..5949785b32 100644
> --- a/iothread.c
> +++ b/iothread.c
> @@ -24,6 +24,8 @@
>  #include "qemu/error-report.h"
>  #include "qemu/rcu.h"
>  #include "qemu/main-loop.h"
> +#include "qapi/clone-visitor.h"
> +#include "qapi/qapi-visit-misc.h"
>  
>  /*
>   * iothread_ref:
> @@ -119,6 +121,25 @@ static void iothread_unref(IOThread *iothread, const IOThreadHolder *holder)
>      object_unref(OBJECT(iothread));
>  }
>  
> +static IOThreadHolderList *iothread_get_holders_list(IOThread *iothread)
> +{
> +    IOThreadHolderList *head = NULL;
> +    IOThreadHolderList **prev = &head;
> +    GList *l;
> +
> +    for (l = iothread->holders; l; l = l->next) {
> +        IOThreadHolder *src = l->data;
> +        IOThreadHolderList *entry = g_new0(IOThreadHolderList, 1);
> +
> +        entry->value = QAPI_CLONE(IOThreadHolder, src);
> +
> +        *prev = entry;
> +        prev = &entry->next;
> +    }

If iothread->holders was a IOThreadHolderList instead of a GList, this
loop could be QAPI_CLONE(IOThreadHolderList, iothread->holders) instead.

> +
> +    return head;
> +}
> +
>  static void *iothread_run(void *opaque)
>  {
>      IOThread *iothread = opaque;
> @@ -488,6 +509,7 @@ static int query_one_iothread(Object *object, void *opaque)
>      info = g_new0(IOThreadInfo, 1);
>      info->id = iothread_get_id(iothread);
>      info->thread_id = iothread->thread_id;
> +    info->holders = iothread_get_holders_list(iothread);
>      info->poll_max_ns = iothread->poll_max_ns;
>      info->poll_grow = iothread->poll_grow;
>      info->poll_shrink = iothread->poll_shrink;
> diff --git a/monitor/hmp-cmds.c b/monitor/hmp-cmds.c
> index 443b8c785d..1b5883147b 100644
> --- a/monitor/hmp-cmds.c
> +++ b/monitor/hmp-cmds.c
> @@ -237,11 +237,37 @@ void hmp_info_iothreads(Monitor *mon, const QDict *qdict)
>      IOThreadInfoList *info_list = qmp_query_iothreads(NULL);
>      IOThreadInfoList *info;
>      IOThreadInfo *value;
> +    IOThreadHolderList *h;
>  
>      for (info = info_list; info; info = info->next) {
>          value = info->value;
>          monitor_printf(mon, "%s:\n", value->id);
>          monitor_printf(mon, "  thread_id=%" PRId64 "\n", value->thread_id);
> +        monitor_printf(mon, "  holders=");
> +        if (value->holders) {
> +            for (h = value->holders; h; h = h->next) {
> +                IOThreadHolder *holder = h->value;
> +
> +                switch (holder->type) {
> +                case IO_THREAD_HOLDER_KIND_BLOCK_NODE:
> +                    monitor_printf(mon, "[block-node: %s]",
> +                                   holder->u.block_node.node_name);
> +                    break;
> +                case IO_THREAD_HOLDER_KIND_QOM_OBJECT:
> +                    monitor_printf(mon, "[qom-path: %s]",
> +                                   holder->u.qom_object.qom_path);
> +                    break;
> +                case IO_THREAD_HOLDER_KIND_MONITOR_NAME:
> +                    monitor_printf(mon, "[monitor-name: %s]",
> +                                   holder->u.monitor_name.monitor_name);
> +                    break;
> +                default:
> +                    monitor_printf(mon, "[unknown]");
> +                    break;
> +                }
> +            }
> +            monitor_printf(mon, "\n");
> +        }
>          monitor_printf(mon, "  poll-max-ns=%" PRId64 "\n", value->poll_max_ns);
>          monitor_printf(mon, "  poll-grow=%" PRId64 "\n", value->poll_grow);
>          monitor_printf(mon, "  poll-shrink=%" PRId64 "\n", value->poll_shrink);
> diff --git a/qapi/misc.json b/qapi/misc.json
> index d9f82f0922..4c16be3fd4 100644
> --- a/qapi/misc.json
> +++ b/qapi/misc.json
> @@ -137,6 +137,13 @@
>  #
>  # @thread-id: ID of the underlying host thread
>  #
> +# @holders: IOThreadHolder of the devices currently associated with

This is rendered like

    • holders ([IOThreadHolder]) – IOThreadHolder of the devices currently associated with

Better use something like

   # @holders: the devices currently associated with ...

I'm not sure about "devices", though.  It's QOM objects, block nodes,
and monitors.  Perhaps the QOM objects are all be devices (subtypes of
TYPE_DEVICE), but I'd have to dig through your patches to be sure.  Does
it matter?

> +#     this iothread.  Users can pre-allocate multiple iothread objects
> +#     to serve as a persistent thread pool.  When a device is
> +#     hot-unplugged, it is detached from its iothread, but the
> +#     iothread remains available, allowing future hot-plugged devices
> +#     to attach to it.  (Since 11.1)

This may need to be rewritten with block nodes and monitors in mind.

> +#
>  # @poll-max-ns: maximum polling time in ns, 0 means polling is
>  #     disabled (since 2.9)
>  #
> @@ -159,6 +166,7 @@
>  { 'struct': 'IOThreadInfo',
>    'data': {'id': 'str',
>             'thread-id': 'int',
> +           'holders': ['IOThreadHolder'],
>             'poll-max-ns': 'int',
>             'poll-grow': 'int',
>             'poll-shrink': 'int',
> @@ -185,6 +193,8 @@
>  #              {
>  #                 "id":"iothread0",
>  #                 "thread-id":3134,
> +#                 "holders":[{"qom-path": "/machine/peripheral/blk1/virtio-backend", "type": "qom-object"},
> +#                            {"qom-path": "/machine/peripheral/blk0/virtio-backend", "type": "qom-object"}],
>  #                 "poll-max-ns":32768,
>  #                 "poll-grow":0,
>  #                 "poll-shrink":0,
> @@ -193,6 +203,7 @@
>  #              {
>  #                 "id":"iothread1",
>  #                 "thread-id":3135,
> +#                 "holders":[{"qom-path": "/machine/peripheral/blk2/virtio-backend", "type": "qom-object"}],
>  #                 "poll-max-ns":32768,
>  #                 "poll-grow":0,
>  #                 "poll-shrink":0,

Would it be useful if one of these examples was a block node?