Re: [Qemu-devel] RFC: virtio-peer shared memory based peer communication device

[Jan Kiszka]

On 2015-09-21 14:13, Michael S. Tsirkin wrote:
> On Fri, Sep 18, 2015 at 06:29:27PM +0200, Claudio Fontana wrote:
>> Hello,
>>
>> this is a first RFC for virtio-peer 0.1, which is still very much a work in 
>> progress:
>>
>> https://github.com/hw-claudio/virtio-peer/wiki
>>
>> It is also available as PDF there, but the text is reproduced here for 
>> commenting:
>>
>> Peer shared memory communication device (virtio-peer)
>>
>> General Overview
>>
>> (I recommend looking at the PDF for some clarifying pictures)
>>
>> The Virtio Peer shared memory communication device (virtio-peer) is a
>> virtual device which allows high performance low latency guest to
>> guest communication. It uses a new queue extension feature tentatively
>> called VIRTIO_F_WINDOW which indicates that descriptor tables,
>> available and used rings and Queue Data reside in physical memory
>> ranges called Windows, each identified with an unique identifier
>> called WindowID.
> 
> So if I had to summarize the difference from regular virtio,
> I'd say the main one is that this uses window id + offset
> instead of the physical address.
> 
> 
> My question is - why do it?
> 
> All windows are in memory space, are they not?
> 
> How about guest using full physical addresses,
> and hypervisor sending the window physical address
> to VM2?
> 
> VM2 can uses that to find both window id and offset.
> 
> 
> This way at least VM1 can use regular virtio without changes.

What would be the value of having different drivers in VM1 and VM2,
specifically if both run Linux?

Jan

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