Hi all!
Here is an asynchronous scheme for handling fragmented qcow2
reads and writes. Both qcow2 read and write functions loops through
sequential portions of data. The series aim it to parallelize these
loops iterations.
It improves performance for fragmented qcow2 images, I've tested it
as follows:
I have four 4G qcow2 images (with default 64k block size) on my ssd disk:
t-seq.qcow2 - sequentially written qcow2 image
t-reverse.qcow2 - filled by writing 64k portions from end to the start
t-rand.qcow2 - filled by writing 64k portions (aligned) in random order
t-part-rand.qcow2 - filled by shuffling order of 64k writes in 1m clusters
(see source code of image generation in the end for details)
and the test (sequential io by 1mb chunks):
test write:
for t in /ssd/t-*; \
do sync; echo 1 > /proc/sys/vm/drop_caches; echo === $t ===; \
./qemu-img bench -c 4096 -d 1 -f qcow2 -n -s 1m -t none -w $t; \
done
test read (same, just drop -w parameter):
for t in /ssd/t-*; \
do sync; echo 1 > /proc/sys/vm/drop_caches; echo === $t ===; \
./qemu-img bench -c 4096 -d 1 -f qcow2 -n -s 1m -t none $t; \
done
short info about parameters:
-w - do writes (otherwise do reads)
-c - count of blocks
-s - block size
-t none - disable cache
-n - native aio
-d 1 - don't use parallel requests provided by qemu-img bench itself
results:
+-----------+-----------+----------+-----------+----------+
| file | wr before | wr after | rd before | rd after |
+-----------+-----------+----------+-----------+----------+
| seq | 8.605 | 8.636 | 9.043 | 9.010 |
| reverse | 9.934 | 8.654 | 17.162 | 8.662 |
| rand | 9.983 | 8.687 | 19.775 | 9.010 |
| part-rand | 9.871 | 8.650 | 14.241 | 8.669 |
+-----------+-----------+----------+-----------+----------+
Performance gain is obvious, especially for read.
how images are generated:
=== gen-writes file ===
#!/usr/bin/env python
import random
import sys
size = 4 * 1024 * 1024 * 1024
block = 64 * 1024
block2 = 1024 * 1024
arg = sys.argv[1]
if arg in ('rand', 'reverse', 'seq'):
writes = list(range(0, size, block))
if arg == 'rand':
random.shuffle(writes)
elif arg == 'reverse':
writes.reverse()
elif arg == 'part-rand':
writes = []
for off in range(0, size, block2):
wr = list(range(off, off + block2, block))
random.shuffle(wr)
writes.extend(wr)
elif arg != 'seq':
sys.exit(1)
for w in writes:
print 'write -P 0xff {} {}'.format(w, block)
print 'q'
=== gen-test-images.sh file ===
#!/bin/bash
IMG_PATH=/ssd
for name in seq reverse rand part-rand; do
IMG=$IMG_PATH/t-$name.qcow2
echo createing $IMG ...
rm -f $IMG
qemu-img create -f qcow2 $IMG 4G
gen-writes $name | qemu-io $IMG
done
Denis V. Lunev (1):
qcow2: move qemu_co_mutex_lock below decryption procedure
Vladimir Sementsov-Ogievskiy (6):
qcow2: bdrv_co_pwritev: move encryption code out of lock
qcow2: split out reading normal clusters from qcow2_co_preadv
qcow2: async scheme for qcow2_co_preadv
qcow2: refactor qcow2_co_pwritev: split out qcow2_co_do_pwritev
qcow2: refactor qcow2_co_pwritev locals scope
qcow2: async scheme for qcow2_co_pwritev
block/qcow2.c | 506 +++++++++++++++++++++++++++++--------
tests/qemu-iotests/026.out | 18 +-
tests/qemu-iotests/026.out.nocache | 20 +-
3 files changed, 415 insertions(+), 129 deletions(-)