biolatency.bt(8)

1biolatency.bt(8)            System Manager's Manual           biolatency.bt(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       The  original  tool, which is retained as "biolatency-kp.bt", currently
19       works by dynamic tracing of the blk_account*() kernel functions,  which
20       will  need  updating  to match any changes to these functions in future
21       kernels versions.
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23       The updated version of the tool utilizes tracepoints instead of kprobes
24       so that it can be compatible with a wide range of kernel versions.
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26       Since this uses BPF, only the root user can use this tool.
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REQUIREMENTS

29       CONFIG_BPF and bpftrace.
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EXAMPLES

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

37       1st, 2nd
38              This is a range of latency, in microseconds  (shown  in  "[...)"
39              set notation).
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41       3rd    A column showing the count of operations in this range.
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43       4th    This is an ASCII histogram representing the count column.
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OVERHEAD

46       Since  block  device  I/O  usually  has  a  relatively low frequency (<
47       10,000/s), the overhead for this tool is expected to be negligible. For
48       high IOPS storage systems, test and quantify before use.
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SOURCE

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

64       Linux
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STABILITY

67       Unstable - in development.
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AUTHOR

70       Brendan Gregg
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