Hi All,
In commit "Add support for doing total latency percentiles" (b599759ba565e7f2f573af364e6da4fe6d556a90), the total latency percentiles option was added. However, some workloads appear broken:
# fio --name=test --ioengine=libaio --direct=1 --rw=randread --iodepth=1 --size=100% --bs=4k --filename=/dev/nvme0n1 --runtime=5s --write_lat_log=test --disable_lat=0 --disable_clat=1 --disable_slat=1 --lat_percentiles=1
test: (g=0): rw=randread, bs=(R) 4096B-4096B, (W) 4096B-4096B, (T) 4096B-4096B, ioengine=libaio, iodepth=1
fio-3.2-66-g67bfe
Starting 1 process
Jobs: 1 (f=1): [r(1)][100.0%][r=351MiB/s,w=0KiB/s][r=89.9k,w=0 IOPS][eta 00m:00s]
test: (groupid=0, jobs=1): err= 0: pid=6879: Mon Dec 4 15:46:04 2017
read: IOPS=89.7k, BW=351MiB/s (368MB/s)(1753MiB/5001msec)
lat (usec): min=9, max=2259, avg=10.67, stdev= 7.66
lat percentiles (nsec):
| 1.00th=[ 0], 5.00th=[ 0], 10.00th=[ 0], 20.00th=[ 0],
| 30.00th=[ 0], 40.00th=[ 0], 50.00th=[ 0], 60.00th=[ 0],
| 70.00th=[ 0], 80.00th=[ 0], 90.00th=[ 0], 95.00th=[ 0],
| 99.00th=[ 0], 99.50th=[ 0], 99.90th=[ 0], 99.95th=[ 0],
| 99.99th=[ 0]
In the above, we try to enable only lat log, so disable clat and slat. The summary output shows lat, but the values are zero.
# fio --name=test --ioengine=libaio --direct=1 --rw=randread --iodepth=1 --size=100% --bs=4k --filename=/dev/nvme0n1 --runtime=5s --write_lat_log=test --disable_lat=0 --disable_clat=0 --disable_slat=1 --lat_percentiles=1
test: (g=0): rw=randread, bs=(R) 4096B-4096B, (W) 4096B-4096B, (T) 4096B-4096B, ioengine=libaio, iodepth=1
fio-3.2-66-g67bfe
Starting 1 process
Jobs: 1 (f=1): [r(1)][100.0%][r=356MiB/s,w=0KiB/s][r=91.1k,w=0 IOPS][eta 00m:00s]
test: (groupid=0, jobs=1): err= 0: pid=6956: Mon Dec 4 15:47:43 2017
read: IOPS=87.8k, BW=343MiB/s (360MB/s)(1715MiB/5001msec)
clat (nsec): min=561, max=2258.3k, avg=9941.30, stdev=6660.37
lat (usec): min=9, max=2259, avg=10.88, stdev= 7.52
lat percentiles (nsec):
| 1.00th=[10304], 5.00th=[10304], 10.00th=[10304], 20.00th=[10304],
| 30.00th=[10432], 40.00th=[10432], 50.00th=[10432], 60.00th=[10432],
| 70.00th=[10432], 80.00th=[10944], 90.00th=[11072], 95.00th=[14784],
| 99.00th=[15296], 99.50th=[15424], 99.90th=[16064], 99.95th=[17024],
| 99.99th=[24704]
In the above, we force clat on, and now the lat values are non-zero in the summary output.
In the commit for stat.c, I see:
if (ts->lat_percentiles)
add_clat_percentile_sample(ts, nsec, ddir);
Does that seem correct?
Regards,
Jeff
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