On 22/01/18 21:19, Christoph Hellwig wrote:

On Wed, Jan 17, 2018 at 08:33:59PM +0100, Heinz Mauelshagen wrote:

quoted

Enhancing IO performance compared to the kernels existing
loop driver thus better suiting respective requirements in
test setups, this patch series adds new "loop" and "ram" targets.

For a fair comparism vs loop you'll need to compare it to the
direct I/O mode.

True, the tested use cases were based  on backing filesystems
w/o direct I/O support which is valuable to me.

   If it is faster than that we have a very serious
bug somewhere.

As a quick test I opened the backing file O_DIRECT in dm-loop on XFS 
backed by
NVMe and it's 10-20% slower than loop because it's bio based and thus 
lags mq.

So, no worries, loop looks ok in regards to direct I/O mode.

quoted

For measures see test results below.


The "loop" target maps segments to backing files.
Mapping table example:
0 4192256 loop /tmp/mapper_loop1
4192256 2097152 loop /dev/nvm/mapper_loop0


The "ram" target accesses RAM directly rather than through
tmpfs additionally enhancing performance compared to "loop"
thus avoding filesystem overhead.
Mapping table example:
0 8388608 ram

"ram" is a singleton target.


Performance test results for 4K and 32K IOPS comparing the loop driver
with dm-loop backed by tmpfs and dm-ram (all 2GiB backing size):

<TESTSCRIPT>
#!/bin/sh
for f in /tmp/loop0 /tmp/mapper_loop0
do
	dd if=/dev/zero of=$f bs=256M count=8 iflag=fullblock
done

losetup /dev/loop0 /tmp/loop0
sectors=`du -s /tmp/mapper_loop0|cut -f1`
dmsetup create loop0 --table "0 $sectors loop /tmp/mapper_loop0"
dmsetup create ram --table "0 $sectors ram"

for bs in 4K 32K
do
	for d in /dev/loop0 /dev/mapper/loop0 /dev/mapper/ram
	do
		echo 3 > /proc/sys/vm/drop_caches
		fio --bs=$bs --rw=randrw --numjobs=99 --group_reporting --iodepth=12 --runtime=3 --ioengine=libaio \
		    --loops=1 --direct=1 --exitall --name dc --filename=$d | egrep "read|write"
	done
done
</TESTSCRIPT>

<4K_RESULTS>
loop driver:
    read: IOPS=226k, BW=881MiB/s (924MB/s)(2645MiB/3003msec)
   write: IOPS=225k, BW=880MiB/s (923MB/s)(2643MiB/3003msec)
dm-loop target:
    read: IOPS=425k, BW=1661MiB/s (1742MB/s)(4990MiB/3004msec)
   write: IOPS=425k, BW=1662MiB/s (1743MB/s)(4992MiB/3004msec)
dm-ram target:
    read: IOPS=636k, BW=2484MiB/s (2605MB/s)(7464MiB/3005msec)
   write: IOPS=636k, BW=2484MiB/s (2605MB/s)(7464MiB/3005msec)
</4K_RESULTS>

<32K_RESULTS>
loop driver:
   read: IOPS=55.5k, BW=1733MiB/s (1817MB/s)(5215MiB/3009msec)
   write: IOPS=55.2k, BW=1726MiB/s (1810MB/s)(5195MiB/3009msec)
dm-loop target:
    read: IOPS=110k, BW=3452MiB/s (3620MB/s)(10.1GiB/3006msec)
   write: IOPS=110k, BW=3448MiB/s (3615MB/s)(10.1GiB/3006msec)
dm-ram target:
    read: IOPS=355k, BW=10.8GiB/s (11.6GB/s)(32.6GiB/3008msec)
   write: IOPS=355k, BW=10.8GiB/s (11.6GB/s)(32.6GiB/3008msec)
</32K_RESULTS>


Signed-off-by: Heinz Mauelshagen <redacted>

Heinz Mauelshagen (2):
   dm loop: new target redirecting io to backing file(s)
   dm ram: new target redirecting io to RAM

  Documentation/device-mapper/loop.txt |  20 ++
  Documentation/device-mapper/ram.txt  |  15 ++
  drivers/md/Kconfig                   |  14 ++
  drivers/md/Makefile                  |   2 +
  drivers/md/dm-loop.c                 | 352 +++++++++++++++++++++++++++++++++++
  drivers/md/dm-ram.c                  | 101 ++++++++++
  6 files changed, 504 insertions(+)
  create mode 100644 Documentation/device-mapper/loop.txt
  create mode 100644 Documentation/device-mapper/ram.txt
  create mode 100644 drivers/md/dm-loop.c
  create mode 100644 drivers/md/dm-ram.c

-- 
2.14.3

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