Zhang Chen <[email protected]> writes:
> On Tue, Feb 17, 2026 at 3:51 PM Markus Armbruster <[email protected]> wrote:
>>
>> Zhang Chen <[email protected]> writes:
>>
>> > Extend the 'IOThreadInfo' structure to include attachment metrics.
>> > This allows users to monitor how many devices are associated with
>> > a specific IOThread and identify them by their QOM paths.
>> >
>> > New fields added to IOThreadInfo:
>> > - @attached-cnt: An integer representing the number of devices
>> > currently using this IOThread's AioContext.
>> > - @attached-dev: A string containing a delimited list ("|") of
>> > QOM paths for the attached devices.
>> >
>> > These fields are also exposed via the Human Monitor Interface (HMP)
>> > command 'info iothreads' to assist with manual debugging and
>> > performance tuning.
>> >
>> > Example QMP output:
>> > {
>> > "id": "iothread0",
>> > "thread-id": 3134,
>> > "attached-cnt": 2,
>> > "attached-dev": "/machine/peripheral/blk1/virtio-backend |
>> > /machine/peripheral/blk0/virtio-backend",
>> > ...
>> > }
>> >
>> > Signed-off-by: Zhang Chen <[email protected]>
>>
>> [...]
>>
>> > diff --git a/qapi/misc.json b/qapi/misc.json
>> > index 1f5062df2a..ca53638684 100644
>> > --- a/qapi/misc.json
>> > +++ b/qapi/misc.json
>> > @@ -76,6 +76,19 @@
>> > #
>> > # @thread-id: ID of the underlying host thread
>> > #
>> > +# @attached-cnt: The parameter is a counter indicating how many
>> > +# active devices are currently associated with this iothread
>> > +# (e.g. virtio-blk). In hotplug scenarios, users can
>> > +# pre-allocate multiple iothread objects to serve as a persistent
>> > +# thread pool. When a device is hot-unplugged, the corresponding
>> > +# IOThread is released but remains available, allowing subsequent
>> > +# hot-plugged devices to attach to and reuse the existing thread.
>> > +# (since 11.0)
>> > +#
>> > +# @attached-dev: A list of QOM paths for the devices currently
>> > +# associated with this IOThread, delimited by " | ".
>> > +# Returns "none" if no devices are attached. (since 11.0)
Does not compile:
In file included from ../qapi/qapi-schema.json:66:
../qapi/misc.json:90:49: Use two spaces between sentences
If this not the end of a sentence, please report a bug.
This error has been in master for almost three months. Is your tree
that far behind?
>>
>> QAPI schema design maxim: do not encode structured data as strings.
>> @attached-devs should be an array of QOM paths instead.
>
> OK, will fix in next version.
Thanks!
>> Unless I misunderstand your docs, @attached-cnt is the number of QOM
>> paths in @attached-dev, i.e. @attached-dev is redundant. If this is the
>> case, drop it. If it isn't, educate me :)
>
> As Stefan's comments, I try to address more specific needs:
> https://mail.gnu.org/archive/html/qemu-devel/2026-02/msg01892.html
As far as I can tell, Stefan asked for the QOM paths of attached
devices. @attached-dev provides it. Good. Why have @attached-cnt as
well?
>> We generally avoid abbreviations in the QAPI schema: @attached-count,
>> @attached-devices.
>>
>> > +#
>> > # @poll-max-ns: maximum polling time in ns, 0 means polling is
>> > # disabled (since 2.9)
>> > #
>> > @@ -93,6 +106,8 @@
>> > { 'struct': 'IOThreadInfo',
>> > 'data': {'id': 'str',
>> > 'thread-id': 'int',
>> > + 'attached-cnt': 'int',
>> > + 'attached-dev': 'str',
>> > 'poll-max-ns': 'int',
>> > 'poll-grow': 'int',
>> > 'poll-shrink': 'int',
>> > @@ -118,6 +133,8 @@
>> > # {
>> > # "id":"iothread0",
>> > # "thread-id":3134,
>> > +# "attached-cnt":2,
>> > +# "attached-dev":/machine/peripheral/blk1/virtio-backend
>> > | /machine/peripheral/blk0/virtio-backend,
>>
>> Once again, the example is syntactically incorrect (the value lacks
>> double quotes), and once again I recommend to create example I/O by
>> actually running a test. Getting tired of this, to be frank.
>
> Sorry for that again. Will fix in next version.
> And I tested this series before send the mail like this:
>
> (qemu) info iothreads
> iothread2:
> thread_id=434428
> attached-cnt=0
> attached-dev=none
> poll-max-ns=32768
> poll-grow=0
> poll-shrink=0
> aio-max-batch=0
> iothread1:
> thread_id=434427
> attached-cnt=2
> attached-dev=/machine/peripheral/blk1/virtio-backend |
> /machine/peripheral/blk0/virtio-backend
> poll-max-ns=32768
> poll-grow=0
> poll-shrink=0
> aio-max-batch=0
You can manually test QMP like this:
$ qemu-system-x86_64 -S -display none -chardev
socket,id=qmp,path=test-qmp,server=on,wait=off -mon mode=control,chardev=qmp
-object iothread,id=iot0
In another terminal:
$ socat "READLINE,history=$HOME/.qmp_history,prompt=QMP> "
UNIX-CONNECT:test-qmp
{"QMP": {"version": {"qemu": {"micro": 50, "minor": 2, "major": 10},
"package": "v10.2.0-1533-g627cf8d1ed-dirty"}, "capabilities": ["oob"]}}
QMP> {"execute": "qmp_capabilities", "arguments": {"enable": ["oob"]}}
{"return": {}}
QMP> {"execute": "query-iothreads"}
{"return": [{"poll-shrink": 0, "thread-id": 2140323, "aio-max-batch": 0,
"attached-dev": "none", "poll-grow": 0, "attached-cnt": 0, "poll-max-ns":
32768, "id": "iot0"}]}
QMP> {"execute": "quit"}
{"timestamp": {"seconds": 1771922506, "microseconds": 801687}, "event":
"SHUTDOWN", "data": {"guest": false, "reason": "host-qmp-quit"}}
{"return": {}}
>> > # "poll-max-ns":32768,
>> > # "poll-grow":0,
>> > # "poll-shrink":0,
>> > @@ -126,6 +143,8 @@
>> > # {
>> > # "id":"iothread1",
>> > # "thread-id":3135,
>> > +# "attached-cnt":1,
>> > +# "attached-dev":/machine/peripheral/blk3/virtio-backend,
>>
>> Likewise.
>
> Thanks
> Chen
>
>>
>> > # "poll-max-ns":32768,
>> > # "poll-grow":0,
>> > # "poll-shrink":0,
>>
