bssplit is off by 8x #1325
Description
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- [ yes ] I have read the GitHub issues section of REPORTING-BUGS.
Description of the bug:
block sizes specified in bssplit are multiplied by 8 as confirmed by blktrace in a sequential write job
Environment:
Ubuntu 20.04.2 LTS
fio version:
Built from master,
/usr/local/bin/fio -version
fio-3.29-7-g01686
Reproduction steps
Config file
cat fio.cfg
[global]
thread=1
ioengine=libaio
direct=1
fadvise_hint=0
group_reporting=1
randrepeat=0
verify=0
time_based=1
runtime=1m
ramp_time=2s
size=100%
[wr-bw]
rw=write
bs=4096
bssplit=4k/72:8k/18:12k/3:16k/7
iodepth=256
numjobs=1
stonewall
NOTE: our desired block size distribution is given by,
bssplit=4k/72:8k/18:12k/3:16k/7
Run
Start blktrace,
blktrace -d /dev/md0 -o blktrace_run.bin
Start fio,
/usr/local/bin/fio --filename="/dev/md0" fio.cfg
Analyze blktrace results
Parse out writes and compute their histogram,
blkparse blktrace_run.bin -a write|awk '/ Q / { if ($7 ~ /W/) print $10 }' |sort |uniq -c |sort -rn >run_writes.txt
Count total number of writes,
cat run_writes.txt|awk '{total += $1} END {print total}'
11230124
Output percentage of block sizes written,
cat run_writes.txt|awk 'BEGIN {total = 11230124; blockSize = 4096} {printf("%d (%f%%)\n", $2*blockSize, 100.0 *($1 / total))}'|head
32768 (72.003301%)
65536 (18.000451%)
131072 (6.994126%)
98304 (3.002122%)
N.B. Percentages are matching up but the block sizes are consistently off by 8x. (I've repeated this several times with different values of bssplit, each time I get the same distribution modulo the scaling of the block sizes by 8).