Re: [Qemu-devel] Towards an ivshmem 2.0?

[msuchanek <msuchanek@suse.de>]

On 2017-01-17 10:59, Stefan Hajnoczi wrote:
> On Mon, Jan 16, 2017 at 02:10:17PM +0100, Jan Kiszka wrote:
>> On 2017-01-16 13:41, Marc-André Lureau wrote:
>> > On Mon, Jan 16, 2017 at 12:37 PM Jan Kiszka <jan.kiszka@siemens.com
>> > <mailto:jan.kiszka@siemens.com>> wrote:
>> >     So, this is our proposal. Would be great to hear some opinions if you
>> >     see value in adding support for such an "ivshmem 2.0" device to QEMU as
>> >     well and expand its ecosystem towards Linux upstream, maybe also DPDK
>> >     again. If you see problems in the new design /wrt what QEMU provides so
>> >     far with its ivshmem device, let's discuss how to resolve them. Looking
>> >     forward to any feedback!
>> >
>> >
>> > My feeling is that ivshmem is not being actively developped in qemu, but
>> > rather virtio-based solutions (vhost-pci for vm2vm).
>> 
>> As pointed out, for us it's most important to keep the design simple -
>> even at the price of "reinventing" some drivers for upstream (at 
>> least,
>> we do not need two sets of drivers because our interface is fully
>> symmetric). I don't see yet how vhost-pci could achieve the same, but
>> I'm open to learn more!
> 
> The concept of symmetry is nice but only applies for communications
> channels like networking and serial.
> 
> It doesn't apply for I/O that is fundamentally asymmetric like disk 
> I/O.
> 
> I just wanted to point this out because lack symmetry has also bothered
> me about virtio but it's actually impossible to achieve it for all
> device types.
> 

What's asymetric about storage? IIRC both SCSI and Firewire which can be
used for storage are symmetric. All asymmetry only comes from usage
convention or less capable buses like IDE/SATA.

Thanks

Michal