Good Morning,
I have a short question about the used io depth reported by Fio/blktrace/iowatcher:
If I am starting a test:
# blktrace -d /dev/sde -o hdd &
# fio --rw=read --name=wd --bs=1024k --direct=1 --filename=/dev/sde --offset=0 --runtime=300 --ioengine=libaio --iodepth=4
[...]
IO depths : 1=0.1%, 2=0.1%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, >=64=0.0%
submit : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
complete : 0=0.0%, 4=100.0%, 8=0.0%, 16=0.0%, 32=0.0%, 64=0.0%, >=64=0.0%
[...]
As seen above Fio is reporting 100% io depth 4. In contrast to that blktrace and iowatcher (cf. attached figure) revealing the following io depths (9 and 7):
# blkparse hdd.blktrace.8
[...]
CPU8 (hdd):
Reads Queued: 9072, 4644MiB Writes Queued: 0, 0KiB
Read Dispatches: 9070, 4643MiB Write Dispatches: 0, 0KiB
Reads Requeued: 0 Writes Requeued: 0
Reads Completed: 9072, 4644MiB Writes Completed: 0, 0KiB
Read Merges: 0, 0KiB Write Merges: 0, 0KiB
Read depth: 9
[...]
# iowatcher -t hdd.blktrace.8 -o wd.svg
(showing an io depth of 7)
Where is this divergence concerning the io depths coming from? A short explanation would be great =)
Best regards, Georg
Attachment:
wd-iowatcher.png
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