Re: [PATCH v2 1/2] qdev: add IOThreadVirtQueueMappingList property type

[Kevin Wolf <kwolf@redhat.com>]

Am 18.09.2023 um 18:16 hat Stefan Hajnoczi geschrieben:
> 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>

When testing this, Qing Wang noticed that "info qtree" crashes. This is
because the string output visitor doesn't support structs. I suppose
IOThreadVirtQueueMapping is the first struct type that is used in a qdev
property type.

So we'll probably have to add some kind of struct support to the string
output visitor before we can apply this. Even if it's as stupid as just
printing "<struct IOThreadVirtQueueMapping>" without actually displaying
the value.

Kevin