is getting more common than it used to be. NVMe is no longer tied to block storage. Command sets in NVMe 2.0 spec opened an excellent way to present non-block interfaces to the Host. ZNS and KV came along with it, and some new command sets are emerging. OTOH, Kernel IO advances historically centered around the block IO path. Passthrough IO path existed, but it stayed far from all the advances, be it new features or performance. Current state & discussion points: --------------------------------- Status-quo changed in the recent past with the new passthrough path (ng char interface + io_uring command). Feature parity does not exist, but performance parity does. Adoption draws asks. I propose a session covering a few voices and finding a path-forward for some ideas too. 1. Command cancellation: while NVMe mandatorily supports the abort command, we do not have a way to trigger that from user-space. There are ways to go about it (with or without the uring-cancel interface) but not without certain tradeoffs. It will be good to discuss the choices in person. 2. Cgroups: works for only block dev at the moment. Are there outright objections to extending this to char-interface IO? 3. DMA cost: is high in presence of IOMMU. Keith posted the work[1], with block IO path, last year. I imagine plumbing to get a bit simpler with passthrough-only support. But what are the other things that must be sorted out to have progress on moving DMA cost out of the fast path? 4. Direct NVMe queues - will there be interest in having io_uring managed NVMe queues? Sort of a new ring, for which I/O is destaged from io_uring SQE to NVMe SQE without having to go through intermediate constructs (i.e., bio/request). Hopefully,that can further amp up the efficiency of IO. 5. <anything else that might be of interest to folks> I hope to send some code/PoC to discuss the stuff better. [1]https://lore.kernel.org/linux-nvme/20220805162444.3985535-1-kbusch@xxxxxx/
