When sqthread_poll is specified for io_uring and io_uring_cmd I/O engines,
fio doesn't report submission latency and the completion latency is too big.
Latency data before:
fio --name=test --size=1M --rw=randread --ioengine=io_uring --sqthread_poll=1
clat (msec): min=1120.1k, max=1120.1k, avg=1120092.65, stdev= 8.32
lat (usec): min=104, max=5312, avg=132.81, stdev=325.05
clat percentiles (msec):
| 1.00th=[17113], 5.00th=[17113], 10.00th=[17113], 20.00th=[17113],
| 30.00th=[17113], 40.00th=[17113], 50.00th=[17113], 60.00th=[17113],
| 70.00th=[17113], 80.00th=[17113], 90.00th=[17113], 95.00th=[17113],
| 99.00th=[17113], 99.50th=[17113], 99.90th=[17113], 99.95th=[17113],
| 99.99th=[17113]
lat (msec) : >=2000=100.00%
As kernel polling thread handles the submission, there is no way to know when
the actual submission happened. We can only rely on the commit hook and
measure the issue time.
Latency data after the change:
fio --name=test --size=1M --rw=randread --ioengine=io_uring --sqthread_poll=1
slat (nsec): min=50, max=2230, avg=146.68, stdev=138.08
clat (usec): min=105, max=5151, avg=132.98, stdev=314.89
lat (usec): min=105, max=5153, avg=133.13, stdev=315.03
clat percentiles (usec):
| 1.00th=[ 106], 5.00th=[ 108], 10.00th=[ 109], 20.00th=[ 110],
| 30.00th=[ 111], 40.00th=[ 113], 50.00th=[ 114], 60.00th=[ 115],
| 70.00th=[ 117], 80.00th=[ 118], 90.00th=[ 119], 95.00th=[ 121],
| 99.00th=[ 123], 99.50th=[ 123], 99.90th=[ 5145], 99.95th=[ 5145],
| 99.99th=[ 5145]
lat (usec) : 250=99.61%
lat (msec) : 10=0.39%
This fixes the issue: https://github.com/axboe/fio/issues/1484
Ankit Kumar (2):
engines:io_uring: slat and clat calculation with sqthread_poll
doc: update about sqthread_poll
HOWTO.rst | 4 +++-
engines/io_uring.c | 4 ++++
fio.1 | 4 +++-
3 files changed, 10 insertions(+), 2 deletions(-)
--
2.17.1
