On 10/12/21 12:31 PM, Keith Busch wrote: > On Tue, Oct 12, 2021 at 12:13:52PM -0600, Jens Axboe wrote: >> 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. >> >> Retain the full clear for the other commands to avoid doing any audits >> there, and just clear the fields in the rw command manually that we >> don't already fill. > > Oo, we knew about this optimization *years* ago, yet didn't do anything > about it! Better late than never. > > http://lists.infradead.org/pipermail/linux-nvme/2014-May/000837.html Dang, 2014! Better late than never... > Acked-by: Keith Busch <kbusch@xxxxxxxxxx> Added, thanks. -- Jens Axboe
