This series shows one way to do what the title says. This puts up a more direct/lean path that enables - submission from io_uring SQE to NVMe SQE - completion from NVMe CQE to io_uring CQE Essentially cutting the hoops (involving request/bio) for nvme io path. Also, io_uring ring is not to be shared among application threads. Application is responsible for building the sharing (if it feels the need). This means ring-associated exclusive queue can do away with some synchronization costs that occur for shared queue. Primary objective is to amp up of efficiency of kernel io path further (towards PCIe gen N, N+1 hardware). And we are seeing some asks too [1]. Building-blocks =============== At high level, series can be divided into following parts - 1. nvme driver starts exposing some queue-pairs (SQ+CQ) that can be attached to other in-kernel user (not just to block-layer, which is the case at the moment) on demand. Example: insmod nvme.ko poll_queus=1 raw_queues=2 nvme0: 24/0/1/2 default/read/poll queues/raw queues While driver registers other queues with block-layer, raw-queues are rather reserved for exclusive attachment with other in-kernel users. At this point, each raw-queue is interrupt-disabled (similar to poll_queues). Maybe we need a better name for these (e.g. app/user queues). [Refer: patch 2] 2. register/unregister queue interface (a) one for io_uring application to ask for device-queue and register with the ring. [Refer: patch 4] (b) another at nvme so that other in-kernel users (io_uring for now) can ask for a raw-queue. [Refer: patch 3, 5, 6] The latter returns a qid, that io_uring stores internally (not exposed to user-space) in the ring ctx. At max one queue per ring is enabled. Ring has no other special properties except the fact that it stores a qid that it can use exclusively. So application can very well use the ring to do other things than nvme io. 3. user-interface to send commands down this way (a) uring-cmd is extended to support a new flag "IORING_URING_CMD_DIRECT" that application passes in the SQE. That is all. (b) the flag goes down to provider of ->uring_cmd which may choose to do things differently based on it (or ignore it). [Refer: patch 7] 4. nvme uring-cmd understands the above flag. It submits the command into the known pre-registered queue, and completes (polled-completion) from it. Transformation from "struct io_uring_cmd" to "nvme command" is done directly without building other intermediate constructs. [Refer: patch 8, 10, 12] Testing and Performance ======================= fio and t/io_uring is modified to exercise this path. - fio: new "registerqueues" option - t/io_uring: new "k" option Good part: 2.96M -> 5.02M nvme io (without this): # t/io_uring -b512 -d64 -c2 -s2 -p1 -F1 -B1 -O0 -n1 -u1 -r4 -k0 /dev/ng0n1 submitter=0, tid=2922, file=/dev/ng0n1, node=-1 polled=1, fixedbufs=1/0, register_files=1, buffered=1, register_queues=0 QD=64 Engine=io_uring, sq_ring=64, cq_ring=64 IOPS=2.89M, BW=1412MiB/s, IOS/call=2/1 IOPS=2.92M, BW=1426MiB/s, IOS/call=2/2 IOPS=2.96M, BW=1444MiB/s, IOS/call=2/1 Exiting on timeout Maximum IOPS=2.96M nvme io (with this): # t/io_uring -b512 -d64 -c2 -s2 -p1 -F1 -B1 -O0 -n1 -u1 -r4 -k1 /dev/ng0n1 submitter=0, tid=2927, file=/dev/ng0n1, node=-1 polled=1, fixedbufs=1/0, register_files=1, buffered=1, register_queues=1 QD=64 Engine=io_uring, sq_ring=64, cq_ring=64 IOPS=4.99M, BW=2.43GiB/s, IOS/call=2/1 IOPS=5.02M, BW=2.45GiB/s, IOS/call=2/1 IOPS=5.02M, BW=2.45GiB/s, IOS/call=2/1 Exiting on timeout Maximum IOPS=5.02M Not so good part: While single IO is fast this way, we do not have batching abilities for multi-io scenario. Plugging, submission and completion batching are tied to block-layer constructs. Things should look better if we could do something about that. Particularly something is off with the completion-batching. With -s32 and -c32, the numbers decline: # t/io_uring -b512 -d64 -c32 -s32 -p1 -F1 -B1 -O0 -n1 -u1 -r4 -k1 /dev/ng0n1 submitter=0, tid=3674, file=/dev/ng0n1, node=-1 polled=1, fixedbufs=1/0, register_files=1, buffered=1, register_queues=1 QD=64 Engine=io_uring, sq_ring=64, cq_ring=64 IOPS=3.70M, BW=1806MiB/s, IOS/call=32/31 IOPS=3.71M, BW=1812MiB/s, IOS/call=32/31 IOPS=3.71M, BW=1812MiB/s, IOS/call=32/32 Exiting on timeout Maximum IOPS=3.71M And perf gets restored if we go back to -c2 # t/io_uring -b512 -d64 -c2 -s32 -p1 -F1 -B1 -O0 -n1 -u1 -r4 -k1 /dev/ng0n1 submitter=0, tid=3677, file=/dev/ng0n1, node=-1 polled=1, fixedbufs=1/0, register_files=1, buffered=1, register_queues=1 QD=64 Engine=io_uring, sq_ring=64, cq_ring=64 IOPS=4.99M, BW=2.44GiB/s, IOS/call=5/5 IOPS=5.02M, BW=2.45GiB/s, IOS/call=5/5 IOPS=5.02M, BW=2.45GiB/s, IOS/call=5/5 Exiting on timeout Maximum IOPS=5.02M Source ====== Kernel: https://github.com/OpenMPDK/linux/tree/feat/directq-v1 fio: https://github.com/OpenMPDK/fio/commits/feat/rawq-v2 Please take a look. [1] https://lore.kernel.org/io-uring/24179a47-ab37-fa32-d177-1086668fbd3d@xxxxxxxxxxxxxxxxx/ Anuj Gupta (5): fs, block: interface to register/unregister the raw-queue io_uring, fs: plumb support to register/unregister raw-queue nvme: wire-up register/unregister queue f_op callback block: add mq_ops to submit and complete commands from raw-queue pci: modify nvme_setup_prp_simple parameters Kanchan Joshi (7): nvme: refactor nvme_alloc_io_tag_set pci: enable "raw_queues = N" module parameter pci: implement register/unregister functionality io_uring: support for using registered queue in uring-cmd nvme: carve out a helper to prepare nvme_command from ioucmd->cmd nvme: submisssion/completion of uring_cmd to/from the registered queue pci: implement submission/completion for rawq commands drivers/nvme/host/core.c | 31 ++- drivers/nvme/host/fc.c | 3 +- drivers/nvme/host/ioctl.c | 234 +++++++++++++++---- drivers/nvme/host/multipath.c | 2 + drivers/nvme/host/nvme.h | 19 +- drivers/nvme/host/pci.c | 409 +++++++++++++++++++++++++++++++-- drivers/nvme/host/rdma.c | 2 +- drivers/nvme/host/tcp.c | 3 +- drivers/nvme/target/loop.c | 3 +- fs/file.c | 14 ++ include/linux/blk-mq.h | 5 + include/linux/fs.h | 4 + include/linux/io_uring.h | 6 + include/linux/io_uring_types.h | 3 + include/uapi/linux/io_uring.h | 6 + io_uring/io_uring.c | 60 +++++ io_uring/uring_cmd.c | 14 +- 17 files changed, 739 insertions(+), 79 deletions(-) -- 2.25.1
