biolatency(8)

1biolatency(8)               System Manager's Manual              biolatency(8)
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NAME

6       biolatency.bt - Block I/O latency as a histogram. Uses bpftrace/eBPF.
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SYNOPSIS

9       biolatency.bt
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DESCRIPTION

12       This  tool  summarizes  time  (latency) spent in block device I/O (disk
13       I/O) as a power-of-2 histogram. This  allows  the  distribution  to  be
14       studied,  including  modes and outliers. There are often two modes, one
15       for device cache hits and one for cache misses, which can be  shown  by
16       this tool. Latency outliers will also be shown.
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18       This tool currently works by dynamic tracing of the blk_account*() ker‐
19       nel functions, which will need updating to match any changes  to  these
20       functions in future kernels versions.
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22       Since this uses BPF, only the root user can use this tool.
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REQUIREMENTS

25       CONFIG_BPF and bpftrace.
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EXAMPLES

28       Trace  block  device  I/O  (disk I/O), and print a latency histogram on
29       Ctrl-C:
30              # biolatency.bt
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FIELDS

33       1st, 2nd
34              This is a range of latency, in microseconds  (shown  in  "[...)"
35              set notation).
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37       3rd    A column showing the count of operations in this range.
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39       4th    This is an ASCII histogram representing the count column.
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OVERHEAD

42       Since  block  device  I/O  usually  has  a  relatively low frequency (<
43       10,000/s), the overhead for this tool is expected to be negligible. For
44       high IOPS storage systems, test and quantify before use.
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SOURCE

47       This is from bpftrace.
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49              https://github.com/iovisor/bpftrace
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51       Also  look  in  the bpftrace distribution for a companion _examples.txt
52       file containing example usage, output, and commentary for this tool.
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54       This is a bpftrace version of the bcc tool of the same  name.  The  bcc
55       tool may provide more options and customizations.
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57              https://github.com/iovisor/bcc
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OS

60       Linux
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STABILITY

63       Unstable - in development.
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AUTHOR

66       Brendan Gregg
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