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.
Acked-by: Keith Busch <kbusch@xxxxxxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
---
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 7944ad52f213..3e691354598c 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -917,8 +917,6 @@ 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))
@@ -928,9 +926,15 @@ 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);
--
2.33.1
