Hi, Guys
I used blktrace to collect IOs traces on a workload. Then replayed it
on the same disk with btreplay, meanwhile I used blktrace to gather
the traces again. I would like to compare the two traces to evaluate
btreplay accuracy. For io direction, io offset, io size, the two
traces were matched. However for the btt output on average component
times across all IOs, the number of request are not matched.
Here is the btt output on the workload:
ALL MIN AVG MAX N
--------------- ------------- ------------- ------------- -----------
Q2Q 0.000000003 0.000227312 0.302266672 438801
Q2G 0.000000368 0.000003045 0.004852484 175920
G2I 0.000000157 0.000001230 0.000056954 175920
Q2M 0.000000123 0.000000404 0.000005004 262882
I2D 0.000000286 0.000010544 0.008151437 175920
M2D 0.000001543 0.000010717 0.003731306 262882
D2C 0.000035010 0.000188685 0.117930905 438801
Q2C 0.000038161 0.000201288 0.117934610 438801
Here is the btt output on the btreplay:
ALL MIN AVG MAX N
--------------- ------------- ------------- ------------- -----------
Q2Q 0.000000001 0.000238955 0.302027673 416343
Q2G 0.000000339 0.000017235 0.144473266 429721
S2G 0.006854780 0.079412795 0.144471318 15
G2I 0.000000023 0.000000579 0.000022893 429666
Q2M 0.000000163 0.000382036 0.028901367 8970
I2D 0.000000336 0.000672347 0.442394220 430233
M2D 0.000000707 0.067473630 0.439112467 7846
D2C 0.000000601 0.001189618 0.179906289 416325
Q2C 0.000000127 0.003043274 0.510393670 416344
Observation:
1. For both traces, blkparse reported 438802 request queued.
2. In the first btt output, seems like the number of Q2C missed one
that 438801 vs. 438802. Other number of events were correct.
3. In the second btt output, all number of events were below 438802.
And some data were misunderstanding. like the number of Q2G was
greater than the number of Q2Q, I2D > Q2C etc. However its blkparse
reported the correct 438802 request queued.
So how to explain the btt result on btreplay? Your comments are appreciated.
Thx, Xuekun
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