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qdev: add IOThreadVirtQueueMappingList property type

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virtio-blk and virtio-scsi devices will need a way to specify the
mapping between IOThreads and virtqueues. At the moment all virtqueues
are assigned to a single IOThread or the main loop. This single thread
can be a CPU bottleneck, so it is necessary to allow finer-grained
assignment to spread the load.

Introduce DEFINE_PROP_IOTHREAD_VQ_MAPPING_LIST() so devices can take a
parameter that maps virtqueues to IOThreads. The command-line syntax for
this new property is as follows:

  --device '{"driver":"foo","iothread-vq-mapping":[{"iothread":"iothread0","vqs":[0,1,2]},...]}'

IOThreads are specified by name and virtqueues are specified by 0-based
index.

It will be common to simply assign virtqueues round-robin across a set
of IOThreads. A convenient syntax that does not require specifying
individual virtqueue indices is available:

  --device '{"driver":"foo","iothread-vq-mapping":[{"iothread":"iothread0"},{"iothread":"iothread1"},...]}'

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-ID: <20231220134755.814917-4-stefanha@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2023-12-20 08:47:54 -05:00 • committed by Kevin Wolf
parent 350147a871
commit cf03a152c5
3 changed files with 80 additions and 0 deletions
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29
qapi/virtio.json
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@ -928,3 +928,32 @@
'data': { 'path': 'str', 'queue': 'uint16', '*index': 'uint16' },
'returns': 'VirtioQueueElement',
'features': [ 'unstable' ] }
##
# @IOThreadVirtQueueMapping:
#
# Describes the subset of virtqueues assigned to an IOThread.
#
# @iothread: the id of IOThread object
#
# @vqs: an optional array of virtqueue indices that will be handled by this
# IOThread. When absent, virtqueues are assigned round-robin across all
# IOThreadVirtQueueMappings provided. Either all IOThreadVirtQueueMappings
# must have @vqs or none of them must have it.
#
# Since: 9.0
##
{ 'struct': 'IOThreadVirtQueueMapping',
'data': { 'iothread': 'str', '*vqs': ['uint16'] } }
##
# @DummyVirtioForceArrays:
#
# Not used by QMP; hack to let us use IOThreadVirtQueueMappingList internally
#
# Since: 9.0
##
{ 'struct': 'DummyVirtioForceArrays',
'data': { 'unused-iothread-vq-mapping': ['IOThreadVirtQueueMapping'] } }