bcc-biosnoop(8)

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

6       biosnoop - Trace block device I/O and print details incl. issuing PID.
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SYNOPSIS

9       biosnoop [-hQ]
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DESCRIPTION

12       This  tools  traces  block device I/O (disk I/O), and prints a one-line
13       summary for each I/O showing various details. These include the latency
14       from the time of issue to the device to its completion, and the PID and
15       process name from when the I/O was first created (which usually identi‐
16       fies the responsible process).
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18       This  uses  in-kernel eBPF maps to cache process details (PID and comm)
19       by I/O request, as well as a starting  timestamp  for  calculating  I/O
20       latency.
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22       This  works  by  tracing various kernel blk_*() functions using dynamic
23       tracing, and will need updating to match any  changes  to  these  func‐
24       tions.
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26       This  makes  use  of a Linux 4.4 feature (bpf_perf_event_output()); for
27       kernels older than 4.4, see the version under tools/old, which uses  an
28       older mechanism
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30       Since this uses BPF, only the root user can use this tool.
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REQUIREMENTS

33       CONFIG_BPF and bcc.
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OPTIONS

36       -h     Print usage message.
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38       -Q     Include a column showing the time spent quueued in the OS.
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EXAMPLES

41       Trace all block device I/O and print a summary line per I/O:
42              # biosnoop
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FIELDS

45       TIME(s)
46              Time  of  the I/O completion, in seconds since the first I/O was
47              seen.
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49       COMM   Cached process name, if present. This usually (but isn't guaran‐
50              teed) to identify the responsible process for the I/O.
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52       PID    Cached  process  ID, if present. This usually (but isn't guaran‐
53              teed) to identify the responsible process for the I/O.
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55       DISK   Disk device name.
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57       T      Type of I/O: R = read, W = write. This is a simplification.
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59       SECTOR Device sector for the I/O.
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61       BYTES  Size of the I/O, in bytes.
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63       QUE(ms)
64              Time the I/O was queued in the OS before  being  issued  to  the
65              device, in milliseconds.
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67       LAT(ms)
68              Time  for the I/O (latency) from the issue to the device, to its
69              completion, in milliseconds.
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OVERHEAD

72       Since block device I/O  usually  has  a  relatively  low  frequency  (<
73       10,000/s), the overhead for this tool is expected to be negligible. For
74       high IOPS storage systems, test and quantify before use.
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SOURCE

77       This is from bcc.
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79              https://github.com/iovisor/bcc
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81       Also look in the bcc distribution for a  companion  _examples.txt  file
82       containing example usage, output, and commentary for this tool.
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OS

85       Linux
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STABILITY

88       Unstable - in development.
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AUTHOR

91       Brendan Gregg
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