On Wed, Feb 20, 2019 at 06:43:46AM -0800, Matthew Wilcox wrote: > What NVMe doesn't have is a way for the host to tell the controller > "Here's a 2MB sized I/O; bytes 40960 to 45056 are most important to > me; please give me a completion event once those bytes are valid and > then another completion event once the entire I/O is finished". > > I have no idea if hardware designers would be interested in adding that > kind of complexity, but this is why we also have I/O people at the same > meeting, so we can get these kinds of whole-stack discussions going.
We have two unused PRP bits, so I guess there's room to define something like a "me first" flag. I am skeptical we'd get committee approval for that or partial completion events, though. I think the host should just split the more important part of the transfer into a separate command. The only hardware support we have to prioritize that command ahead of others is with weighted priority queues, but we're missing driver support for that at the moment.
