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Demonstrations of bitesize, the Linux perf_events version.
bitesize traces block I/O issued, and reports a histogram of I/O size. By
default five buckets are used to gather statistics on common I/O sizes:
# ./bitesize
Tracing block I/O size (bytes), until Ctrl-C...
^C
Kbytes : I/O Distribution
-> 0.9 : 0 | |
1.0 -> 7.9 : 38 |# |
8.0 -> 63.9 : 10108 |######################################|
64.0 -> 127.9 : 13 |# |
128.0 -> : 1 |# |
In this case, most of the I/O was between 8 and 63.9 Kbytes. The "63.9"
really means "less than 64".
Specifying custom buckets to examine the I/O size in more detail:
# ./bitesize -b "8 16 24 32"
Tracing block I/O size (bytes), until Ctrl-C...
^C
Kbytes : I/O Distribution
-> 7.9 : 89 |# |
8.0 -> 15.9 : 14665 |######################################|
16.0 -> 23.9 : 657 |## |
24.0 -> 31.9 : 661 |## |
32.0 -> : 376 |# |
The I/O is mostly between 8 and 15.9 Kbytes
It's probably 8 Kbytes. Checking:
# ./bitesize -b "8 9"
Tracing block I/O size (bytes), until Ctrl-C...
^C
Kbytes : I/O Distribution
-> 7.9 : 62 |# |
8.0 -> 8.9 : 11719 |######################################|
9.0 -> : 1358 |##### |
It is.
The overhead of this tool is relative to the number of buckets used, hence only
using what is necessary.
To study this I/O in more detail, I can use iosnoop(8) and capture it to a file
for post-processing.
Use -h to print the USAGE message:
# ./bitesize -h
USAGE: bitesize [-h] [-b buckets] [seconds]
-b buckets # specify histogram buckets (Kbytes)
-h # this usage message
eg,
bitesize # trace I/O size until Ctrl-C
bitesize 10 # trace I/O size for 10 seconds
bitesize -b "8 16 32" # specify custom bucket points
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