Re: [PATCH for-next v3 0/4] fixed-buffer for uring-cmd/passthrough

Jens Axboe
2022-09-02T16:06:44Z

On 9/2/22 9:16 AM, Kanchan Joshi wrote:
> Hi,
>
> Currently uring-cmd lacks the ability to leverage the pre-registered
> buffers. This series adds the support in uring-cmd, and plumbs
> nvme passthrough to work with it.
>
> Using registered-buffers showed peak-perf hike from 1.85M to 2.17M IOPS
> in my setup.
>
> Without fixedbufs
> *****************
> # taskset -c 0 t/io_uring -b512 -d128 -c32 -s32 -p0 -F1 -B0 -O0 -n1 -u1 /dev/ng0n1
> submitter=0, tid=5256, file=/dev/ng0n1, node=-1
> polled=0, fixedbufs=0/0, register_files=1, buffered=1, QD=128
> Engine=io_uring, sq_ring=128, cq_ring=128
> IOPS=1.85M, BW=904MiB/s, IOS/call=32/31
> IOPS=1.85M, BW=903MiB/s, IOS/call=32/32
> IOPS=1.85M, BW=902MiB/s, IOS/call=32/32
> ^CExiting on signal
> Maximum IOPS=1.85M

With the poll support queued up, I ran this one as well. tldr is:

bdev (non pt) 122M IOPS
irq driven 51-52M IOPS
polled 71M IOPS
polled+fixed 78M IOPS

Looking at profiles, it looks like the bio is still being allocated
and freed and not dipping into the alloc cache, which is using a
substantial amount of CPU. I'll poke a bit and see what's going on...

--
Jens Axboe