### Motivation
Currently, the relationship between IOThreads and the resources using them is
opaque. From a management perspective, it is difficult to determine which
devices or block exports are currently associated with a specific IOThread
via QMP or HMP.
This series introduces a "holder" tracking mechanism based on QOM paths or
block exports to significantly improve IOThread observability.
In high-performance virtualization environments, users often pre-allocate
a set of IOThreads to serve as a persistent thread pool. During device
hotplug/unplug cycles, while IOThread objects remain persistent,
their attachment state changes dynamically.
By tracking these "holders," administrators can use `query-iothreads` to
monitor the real-time load distribution of the thread pool and identify which
specific devices (e.g., virtio-blk, BlockExport) are attached to which thread.
### Technical Overview
* Holder tracking
Add a QAPI holder list to each IOThread. A holder identifies either
a QOM object by its canonical path or a block export by its unique
BlockExportOptions ID.
* Explicit reference lifecycle
Add iothread_ref_and_get_aio_context() and the matching
iothread_unref_and_put_aio_context(). Acquiring an AioContext registers a
holder and keeps the IOThread alive until the matching put.
Legacy callers without a matching lifecycle use the explicitly named
iothread_unsafe_get_aio_context(). The ambiguous legacy
iothread_get_aio_context() is removed after all production callers
are migrated.
* Subsystem integration
Track holders for block exports, monitors, virtio-blk, virtio-scsi,
virtio queue mappings, virtio balloon thread pinning, COLO compare,
vfio-user proxy, and xen-block.
* Introspection
Extend IOThreadInfo with a holders array returned by
query-iothreads. Display the same information with info iothreads,
while omitting the holders line when the list is empty.
### V12 -> V11 Changelog
- Change the function name from the "iothread_put_aio_context()"
to "iothread_unref_and_put_aio_context()" match the
"iothread_unref_and_put_aio_context".
- Fix unnecessary char * cast since the holder variable is
declared const.
- Add detailed commit msg in patch 06/15.
- Optimize the HMP print in patch 13/15.
- Rebase code on upstream.
### V11 -> V10 Changelog
- Keep iothread_ref_and_get_aio_context() as an explicit acquiring API
instead of merging it into iothread_get_aio_context().
- Retain iothread_get_aio_context() during the caller migration so
every intermediate patch builds, then remove it in patch 14.
- Update patch 15 to use the holder-aware get/put API in unit-test
stubs and callers.
- Rework patch 2 documentation to describe holders as QOM objects or
block exports, simplify the ref/unref descriptions, and use
imperative function comments.
- Identify block export holders with BlockExportOptions member id and
rename the QAPI field to export-id.
- Fix monitor cleanup so it only releases an AioContext acquired by
that monitor, preventing an iothread_unref() assertion at shutdown.
- Rebase the series onto the current upstream tree.
### V10 -> V9 Changelog
- Rebase this series on the Daniel P. Berrangé's series:
[PATCH v7 00/35] monitor: turn QMP and HMP into QOM objects
https://lore.kernel.org/qemu-devel/[email protected]/
- Remove the monitor type of IOThreadHolder, make the monitor as a QOM object.
- Remove GList related code and stays within QAPI instead of mixing GList and
QAPI.
- Fix missed comments in the patch 2.
- Rewrite parts of commit log generated by AI.
- Keep Stefan's reviewed-by in patch 2 and addressed Markus's comments.
- Rewrite parts of code comments.
- Drop original patch 6/7/8 for monitor parts.
### V9 -> V8 Changelog
- Drop to assign unique default ID for monitor, and keep the NULL ID.
- Rewrite and split the monitor patch 7 and 8.
- Add the [PATCH 17/17]tests/unit/iothread: Update the
iothread_get_aio_context
to keep the API same in the unit tests.
- Refactorcode according comments.
- Update the example.
- Fix other comments issues.
### V7 -> V8 Changelog
- Drop the assumption of the Monitor QOM, add the new type
IO_THREAD_HOLDER_KIND_MONITOR_NAME.
- Drop the assumption of the string '/' as QOM path.
- Introduce new patch for Monitor:
[PATCH 06/15] assign unique default ID to anonymous monitors
- Fixed Monitor ID for the IOThread.
- Refactorcode according comments.
- Update QMP example.
- Rebased patches on upstream code.
- Fixed comments issues.
- Removed redundant code.
### V6 -> V7 Changelog
- Fixed comments issues in patch 02/14 (Thanks Markus).
- Removed redundant code.
- Rebased patches on upstream code.
- Fixed code conflict with latest patches.
- Added detailed description in git log and code.
- Added comments for patch 06/14 assuming the monitor is a QOM object,
Depends on Daniel Berrange's RFC patch:
[PATCH RFC 00/17] monitor: turn QMP and HMP into QOM objects
### V5 -> V6 Changelog
* API Refactoring (Breaking Change):
- Implement the 'union': 'IoThreadHolder' for combine the QOM objects
and the block-node.
- Completely merged iothread_get_aio_context variants.
- The iothread_get_aio_context function now strictly requires a 'holder'
argument to ensure every context retrieval is accounted for.
* Expanded Module Coverage:
- Added holder tracking for the monitor subsystem (tracking threads used
by QMP/HMP).
- Added support for the virtio-scsi dataplane.
* Code Cleanup:
- Removed redundant and obsolete API declarations.
- Standardized the use of object_get_canonical_path() across all callers
to provide consistent and unique holder names.
* Bug Fixes:
- Updated qapi/misc.json documentation to fix missing descriptions in
query-iothreads items.
* Build System:
- Improved header inclusion logic to avoid redundant declaration errors
in unit tests.
* QAPI part:
- Sorry to drop the "Acked-by: Markus Armbruster <[email protected]>",
because this version have lots of changes in the:
[PATCH V6 13/14]qapi: examine IOThread attachment status via query-iothreads
Zhang Chen (15):
qapi/misc: Fix missed query-iothreads items
iothread: introduce holder tracking
iothread: track users with holder name
iothread: introduce iothread_unsafe_get_aio_context()
block/export: track IOThread references
monitor: track IOThread users with QOM paths
virtio-vq-mapping: track iothread-vq-mapping references using device
path
virtio: track IOThread references for thread pinning
net/colo: track IOThread references using path-based holder
virtio-balloon: Update tracking iothread users with holder
vfio-user/proxy: Update tracking iothread users with holder name
xen-block: Update tracking iothread users with holder name
monitor/hmp: display IOThread holders
iothread: remove legacy iothread_get_aio_context()
tests/unit/iothread: update AioContext ref/put helpers
block/export/export.c | 79 +++++++++++++++++++---
blockdev.c | 2 +-
hw/block/dataplane/xen-block.c | 19 +++++-
hw/block/virtio-blk.c | 21 ++++--
hw/scsi/virtio-scsi-dataplane.c | 22 ++++--
hw/vfio-user/proxy.c | 16 ++++-
hw/virtio/iothread-vq-mapping.c | 20 ++++--
hw/virtio/virtio-balloon.c | 22 ++++--
include/block/export.h | 6 ++
include/hw/virtio/iothread-vq-mapping.h | 6 +-
include/system/iothread.h | 38 ++++++++++-
iothread.c | 89 ++++++++++++++++++++++++-
monitor/hmp-cmds.c | 21 ++++++
monitor/monitor-internal.h | 3 +
monitor/monitor.c | 26 ++++++--
monitor/qmp.c | 16 ++++-
net/colo-compare.c | 29 +++++---
qapi/misc.json | 86 ++++++++++++++++++++++--
tests/unit/iothread.c | 18 +++--
tests/unit/iothread.h | 7 +-
tests/unit/test-aio-multithread.c | 5 +-
tests/unit/test-bdrv-drain.c | 18 +++--
tests/unit/test-block-iothread.c | 21 ++++--
23 files changed, 508 insertions(+), 82 deletions(-)
--
2.54.0
