Re: [Qemu-devel] [PATCH v1 00/11] memory-device: complete refactoring

[David Hildenbrand <david@redhat.com>]

On 23.07.2018 16:23, Igor Mammedov wrote:
> On Thu,  5 Jul 2018 13:59:32 +0200
> David Hildenbrand <david@redhat.com> wrote:
> 
>> This is another part of the original series
>>     [PATCH v4 00/14] MemoryDevice: use multi stage hotplug handlers
>> And is based on
>>     [PATCH v3 0/4] pc-dimm: pre_plug "slot" and "addr" assignment
>>
>> This series completes refactoring of pre_plug, plug and unplug logic of
>> memory devices. With this as a basis, one can easily have e.g. virtio
>> based memory devices (virtio-mem, virtio-pmem, virtio-fs?) with minor
>> modifications on e.g. x86 and s390x.
>>
>> Unfortunately, the "addr" property is already used for virtio devices, so
>> we will have to deal with device specific properties. So
>> set_addr() for memory devices is introduced to handle that (we already
>> have get_addr()).
>>
>> The only way I see to avoid that would be for virtio based devices to
>> introduce an indirection:
>>
>> E.g. right now for my virtio-mem prototype:
>> ... -object memory-backend-ram,id=mem0,size=8G \
>>     -device virtio-mem-pci,id=vm0,memdev=mem0,node=0,phys-addr=0x12345
> Though it seems inconvenient to have different property name,
> it is not dimm device (even though it shares GPA resource)
> so it is fine for it to have it's own set of properties.
> (might make error reporting a bit ugly)

Same opinion here, that's why I prefer this approach.

> 
> Also what about usecase of mmio based virtio (ARM)?

Can you elaborate?

> 
> 
>> To something like:
>> ... -object memory-backend-ram,id=mem0,size=8G \
>>     -object virtio-mem-backend,id=vmb0,memdev=mem0,addr=0x12345 \
>>     -device virtio-mem-pci,id=vm0,vmem=vmb0 \
> it's broken conceptually,
> backends should deal only with host resource allocation while
> 'addr' is device model property and belongs to a frontend.

Agreed.

> 
>> Or something like (that might be interesting for virtio-pmem):
>> ... -device virtio-mem-pci \ /* a virtio-mem bus */
>>     -object memory-backend-ram,id=mem0,size=8G \
>>     -device virtio-mem-backend,memdev=mem0,addr=0x12345 \
> did you mean  ^^^^ virtio-pmem device?
> 
> Is it a separate controller and memory resource design
> connected together somehow?

Yes, for this example s/mem/pmem/ of course (copy paste). virtio-mem and
virtio-pmem are two separate device types with their own set of
controllers (if any).

I favor the original approach (above).


-- 

Thanks,

David / dhildenb