On 4/5/22 02:33, Bean Huo wrote:
For performance improvement, according to my test, if we abandon SCSI
command parsing, we can get 3%~5% performance improvement. Maybe this
is little or no improvement? Yes, reliability issues outweigh this
performance improvement. Error handling and UFS probes should also be
rebuilt. But most importantly, it makes UFS more scalable. How do you
think about adding an immature development driver to drever/staging
first? name it driver/staging/lightweight-ufs?
I do not understand the interest in bypassing the SCSI core. The
scsi_debug driver supports more than a million IOPS on a single CPU core
(see also the attached script). I think this shows that the SCSI core is
not a performance bottleneck. Additionally, I think it will take a while
until UFS devices scale from the current performance level (100K IOPS?)
to more than a million IOPS.
Please note that bypassing the SCSI core would make it much harder than
necessary to introduce zoned storage support and also that this would
lead to plenty of duplicated code.
For other SCSI LLDs the cost of
atomic operations and memory barriers in the LLD outweighs the cost
of
the operations in the SCSI core and sd drivers. I'm not sure whether
that's also the case for the UFS driver.
I didn't take this into account, maybe it's not a big deal, since the
UFS driver might use its own lock/serialization lock.
Every single atomic operation in the hot path has a measurable
performance impact. That includes locking operations.
Thanks,
Bart.
#!/bin/bash
set -e
iodepth=${1:-1}
runtime=30
blocksize=512
numcpus=$(nproc)
modprobe -r scsi_debug
modprobe scsi_debug max_queue=128 submit_queues="$numcpus" delay=0 fake_rw=1 &&
udevadm settle
DEVICE=$(find /sys/bus/pseudo/drivers/scsi_debug/adapter*/host*/target*/*/block/ -maxdepth 1 -type d | grep -v 'block/$' | head -1 | xargs basename) || exit $?
[ -n "$DEVICE" ] || exit $?
args=()
if [ "$iodepth" = 1 ]; then
args+=(--ioengine=psync)
else
args+=(--ioengine=io_uring --iodepth_batch=$((iodepth/2)) --hipri=1)
fi
args+=(
--bs="${blocksize}"
--direct=1
--filename=/dev/"$DEVICE"
--group_reporting=1
--gtod_reduce=1
--invalidate=1
--iodepth="$iodepth"
--ioscheduler=none
--name=scsi_debug
--numjobs=1
--runtime="$runtime"
--rw=read
--thread
--time_based=1
)
set -x
if numactl -m 0 -N 0 echo >&/dev/null; then
numactl -m 0 -N 0 -- fio "${args[@]}"
else
fio "${args[@]}"
fi
