Re: [RFC 0/8] Copy Offload with Peer-to-Peer PCI Memory

Logan Gunthorpe
2017-04-25T17:03:27Z

On 25/04/17 12:30 AM, Knut Omang wrote:
> Yes, that's why I used 'significant'. One good thing is that given resources
> it can easily be done in parallel with other development, and will give additional
> insight of some form.

Yup, well if someone wants to start working on an emulated RDMA device
that actually simulates proper DMA transfers that would be great!

>> I also imagine it would be quite difficult to develop those models
>> given the array of hardware that needs to be supported and the deep
>> functional knowledge required to figure out appropriate restrictions.
>
> From my naive perspective it seems it need not even be a full model to get some benefits,
> just low level functionality tests with some instances of a
> device that offers some MMIO space 'playground'.

Yes, the nvme device in qemu has a CMB buffer which is a good choice to
test with but we don't have code to use it for p2p transfers in the
kernel so it is a bit awkward. We also posted [1] to qemu which was also
handy to test with using a small out of tree module. But I don't see a
lot of value in it if you completely ignore any hardware quirks.

Logan

[1] https://lists.gnu.org/archive/html/qemu-devel/2016-10/msg04331.html