From a9a7e30fd918588bc312ba782426e3a1282df359 Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Mon, 18 Oct 2021 06:47:18 -0600 Subject: [PATCH] nvme: don't memset() the normal read/write command This memset in the fast path costs a lot of cycles on my setup. Here's a top-of-profile of doing ~6.7M IOPS: + 5.90% io_uring [nvme] [k] nvme_queue_rq + 5.32% io_uring [nvme_core] [k] nvme_setup_cmd + 5.17% io_uring [kernel.vmlinux] [k] io_submit_sqes + 4.97% io_uring [kernel.vmlinux] [k] blkdev_direct_IO and a perf diff with this patch: 0.92% +4.40% [nvme_core] [k] nvme_setup_cmd reducing it from 5.3% to only 0.9%. This takes it from the 2nd most cycle consumer to something that's mostly irrelevant. Reviewed-by: Chaitanya Kulkarni Reviewed-by: Keith Busch Signed-off-by: Jens Axboe --- drivers/nvme/host/core.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c index 824790b..c415c3f 100644 --- a/drivers/nvme/host/core.c +++ b/drivers/nvme/host/core.c @@ -929,8 +929,6 @@ static inline blk_status_t nvme_setup_rw(struct nvme_ns *ns, u16 control = 0; u32 dsmgmt = 0; - memset(cmnd, 0, sizeof(*cmnd)); - if (req->cmd_flags & REQ_FUA) control |= NVME_RW_FUA; if (req->cmd_flags & (REQ_FAILFAST_DEV | REQ_RAHEAD)) @@ -940,9 +938,15 @@ static inline blk_status_t nvme_setup_rw(struct nvme_ns *ns, dsmgmt |= NVME_RW_DSM_FREQ_PREFETCH; cmnd->rw.opcode = op; + cmnd->rw.flags = 0; cmnd->rw.nsid = cpu_to_le32(ns->head->ns_id); + cmnd->rw.rsvd2 = 0; + cmnd->rw.metadata = 0; cmnd->rw.slba = cpu_to_le64(nvme_sect_to_lba(ns, blk_rq_pos(req))); cmnd->rw.length = cpu_to_le16((blk_rq_bytes(req) >> ns->lba_shift) - 1); + cmnd->rw.reftag = 0; + cmnd->rw.apptag = 0; + cmnd->rw.appmask = 0; if (req_op(req) == REQ_OP_WRITE && ctrl->nr_streams) nvme_assign_write_stream(ctrl, req, &control, &dsmgmt); -- 2.7.4