biostacks.bt(8)

1biostacks.bt(8)             System Manager's Manual            biostacks.bt(8)
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NAME

6       biostacks - Show disk I/O latency with initialization stacks. Uses bpf‐
7       trace/eBPF.
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SYNOPSIS

10       biostacks
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DESCRIPTION

13       This tool shows disk I/O latency histograms for each block I/O initial‐
14       ization  path. This can help reveal the reason for different latencies,
15       as some may be created by log flushing, others  by  application  reads,
16       etc.
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18       This  works by tracing the blk_account_io_start() and the blk_start_re‐
19       quest() or blk_mq_start_request() functions using dynamic  instrumenta‐
20       tion.    Linux   5.0   removed   the  classic  I/O  scheduler,  so  the
21       blk_start_request() probe can be removed from  the  tool  (just  delete
22       it).  This  tool  may  need  other maintenance to keep working if these
23       functions change in later kernels.
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25       Since this uses BPF, only the root user can use this tool.
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REQUIREMENTS

28       CONFIG_BPF and bpftrace.
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EXAMPLES

31       Trace disk I/O latency with initialization stacks:
32              # biostacks.bt
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FIELDS

35       0th    An initialization kernel stack  trace  (shown  in  "@[...]")  is
36              printed before each I/O histogram.
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38       1st, 2nd
39              This  is  a  range  of  I/O  latency,  in microseconds (shown in
40              "[...)" set notation).
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42       3rd    A column showing the count of I/O in this range.
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44       4th    This is an ASCII histogram representing the count column.
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OVERHEAD

47       The rate of biostacks should be low (bounded by device IOPS), such that
48       the overhead of this tool is expected to be negligible.
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SOURCE

51       This  tool  originated from the book "BPF Performance Tools", published
52       by Addison Wesley (2019):
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54              http://www.brendangregg.com/bpf-performance-tools-book.html
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56       See the book for more documentation on this tool.
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58       This version is in the bpftrace repository:
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60              https://github.com/iovisor/bpftrace
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62       Also look in the bpftrace distribution for  a  companion  _examples.txt
63       file containing example usage, output, and commentary for this tool.
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OS

66       Linux
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STABILITY

69       Unstable - in development.
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AUTHOR

72       Brendan Gregg
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