Re: [PATCH] Make virtio devices multi-function

[Anthony Liguori <anthony@codemonkey.ws>]

Avi Kivity wrote:
> Anthony Liguori wrote:
>>
>> I think we need to decide what we want to target in terms of upper 
>> limits.
>>
>> With a bridge or two, we can probably easily do 128.
>>
>> If we really want to push things, I think we should do a PCI based 
>> virtio controller.  I doubt a large number of PCI devices is ever 
>> going to perform very well b/c of interrupt sharing and some of the 
>> assumptions in virtio_pci.
>>
>> If we implement a controller, we can use a single interrupt, but 
>> multiplex multiple notifications on that single interrupt.  We can 
>> also be more aggressive about using shared memory instead of PCI 
>> config space which would reduce the overall number of exits.
>>
>> We could easily support a very large number of devices this way.  But 
>> again, what do we want to target for now? 
>
> I think that for networking we should keep things as is.  I don't see 
> anybody using 100 virtual NICs.
>
> For mass storage, we should follow the SCSI model with a single device 
> serving multiple disks, similar to what you suggest.  Not sure if the 
> device should have a single queue or one queue per disk.

My latest thought it to do a virtio-based virtio controller.

We could avoid creating one in QEMU unless we detect an abnormally large 
number of disks or something.

Regards,

Anthony Liguori


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