I'm trying to capture IO traces and average access times (by which I
mean time spent by the hardware and firmware). btt seems to give me
incorrect time for D2C, though. As I understand it, it's saying the
average access time is 0.3ms, while iostat says it's 8.25ms. Am I
misusing the tool somehow? How can I get it to report the data I
want?
Here's how I get my data:
blktrace -d /dev/sdb -o $TRACE.rawtrace
blkparse $TRACE.rawtrace -O -d $TRACE.bin
btt -i $TRACE.bin
This is what btt reports:
==================== All Devices ====================
ALL MIN AVG MAX N
--------------- ------------- ------------- ------------- -----------
Q2Q 0.000003631 0.006093295 5.546805679 13446
Q2G 0.000002235 0.000004725 0.000134377 6893
G2I 0.000001676 0.000118613 0.047795413 9166
Q2M 0.000001676 0.000002203 0.000071798 6554
I2D 0.000008661 0.003768198 0.048250506 7158
M2D 0.000019835 0.000142260 0.016255688 6799
D2C 0.000136332 0.000326485 0.005760325 13447
Q2C 0.000159799 0.002395819 0.048427905 13447
This is what iostat reports:
Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s
avgrq-sz avgqu-sz await svctm %util
sdb 0.00 91.00 0.00 120.00 0.00 1476.00
12.30 0.99 8.25 8.25 99.00
(iostat was reporting every 2 seconds, so its totals won't match the
btt totals, but the averages should match.)
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