On Wed, Apr 12, 2023 at 06:56:15PM +0530, Kanchan Joshi wrote: > On Wed, Apr 12, 2023 at 10:33:40AM +0800, Ming Lei wrote: > > On Wed, Apr 12, 2023 at 04:18:16AM +0530, Kanchan Joshi wrote: > > > > > 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. > > > > > > > > This is interesting, and I've pondered something like that before too. I > > > > think it's worth investigating and hacking up a prototype. I recently > > > > had one user of IOPOLL assume that setting up a ring with IOPOLL would > > > > automatically create a polled queue on the driver side and that is what > > > > would be used for IO. And while that's not how it currently works, it > > > > definitely does make sense and we could make some things faster like > > > > that. It would also potentially easier enable cancelation referenced in > > > > #1 above, if it's restricted to the queue(s) that the ring "owns". > > > > > > So I am looking at prototyping it, exclusively for the polled-io case. > > > And for that, is there already a way to ensure that there are no > > > concurrent submissions to this ring (set with IORING_SETUP_IOPOLL > > > flag)? > > > That will be the case generally (and submissions happen under > > > uring_lock mutex), but submission may still get punted to io-wq > > > worker(s) which do not take that mutex. > > > So the original task and worker may get into doing concurrent submissions. > > > > It seems one defect for uring command support, since io_ring_ctx and > > io_ring_submit_lock() can't be exported for driver. > > Sorry, did not follow the defect part. > io-wq not acquring uring_lock in case of uring-cmd - is a defect? The same > happens for direct block-io too. > Or do you mean anything else here? Maybe defect isn't one accurate word here. I meant ->uring_cmd() is the only driver/fs callback in which issue_flags is exposed, so IO_URING_F_UNLOCKED is visible to driver, but io_ring_submit_lock() can't be done inside driver. No such problem for direct io since the above io_uring details isn't exposed to direct io code. Thanks, Ming
