Re: [PATCH] blk-mq: allow hardware queue to get more tag while sharing a tag set

[Bart Van Assche]

On 8/5/21 6:50 PM, yukuai (C) wrote:
> After applying this configuration, the number of null_blk in my
> machine is about 650k(330k before). Is this still too low?

That seems low to me. If I run the attached script on a six year old
desktop with an eight core i7-4790 CPU it reports a little more than 5
million IOPS. Has kernel debugging perhaps been enabled in the kernel on
the test setup? Or is the system perhaps slowed down by security
mitigations?

> By the way, there are no performance degradation.

Please wait with drawing a conclusion until you can run a workload on
your setup of several million IOPS.

Thanks,

Bart.
#!/bin/bash

if [ -e /sys/kernel/config/nullb ]; then
    for d in /sys/kernel/config/nullb/*; do
        [ -d "$d" ] && rmdir "$d"
    done
fi
numcpus=$(grep -c ^processor /proc/cpuinfo)
modprobe -r null_blk
[ -e /sys/module/null_blk ] && exit $?
modprobe null_blk nr_devices=0 &&
    udevadm settle &&
    cd /sys/kernel/config/nullb &&
    mkdir nullb0 &&
    cd nullb0 &&
    echo 0 > completion_nsec &&
    echo 512 > blocksize &&
    echo 0 > home_node &&
    echo 0 > irqmode &&
    echo 1024 > size &&
    echo 0 > memory_backed &&
    echo 2 > queue_mode &&
    echo 1 > power ||
    exit $?

(
    cd /sys/block/nullb0/queue &&
	echo 2 > rq_affinity
) || exit $?

iodepth=${1:-1}
runtime=30
args=()
if [ "$iodepth" = 1 ]; then
	args+=(--ioengine=psync)
else
	args+=(--ioengine=io_uring --iodepth_batch=$((iodepth/2)))
fi
args+=(--iodepth=$iodepth --name=nullb0 --filename=/dev/nullb0\
    --rw=read --bs=4096 --loops=$((1<<20)) --direct=1 --numjobs=$numcpus \
    --thread --runtime=$runtime --invalidate=1 --gtod_reduce=1 \
    --group_reporting=1 --ioscheduler=none)
if numactl -m 0 -N 0 echo >&/dev/null; then
	numactl -m 0 -N 0 -- fio "${args[@]}"
else
	fio "${args[@]}"
fi