bcc-biolatency(8)

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

6       biolatency - Summarize block device I/O latency as a histogram.
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SYNOPSIS

9       biolatency  [-h] [-F] [-T] [-Q] [-m] [-D] [-F] [-e] [-j] [-d DISK] [in‐
10       terval [count]]
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DESCRIPTION

13       biolatency traces block device I/O (disk I/O), and records the  distri‐
14       bution  of I/O latency (time). This is printed as a histogram either on
15       Ctrl-C, or after a given interval in seconds.
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17       The latency of disk I/O operations is measured from when  requests  are
18       issued  to  the device up to completion. A -Q option can be used to in‐
19       clude time queued in the kernel.
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21       This tool uses in-kernel eBPF maps for storing timestamps and the  his‐
22       togram, for efficiency.
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24       This  works  by  tracing various kernel blk_*() functions using dynamic
25       tracing, and will need updating to match any  changes  to  these  func‐
26       tions.
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28       Since this uses BPF, only the root user can use this tool.
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REQUIREMENTS

31       CONFIG_BPF and bcc.
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OPTIONS

34       -h Print usage message.
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36       -T     Include timestamps on output.
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38       -m     Output histogram in milliseconds.
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40       -D     Print a histogram per disk device.
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42       -F     Print a histogram per set of I/O flags.
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44       -j     Print a histogram dictionary
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46       -e     Show extension summary(total, average)
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48       -d DISK
49              Trace this disk only
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51       interval
52              Output interval, in seconds.
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54       count  Number of outputs.
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EXAMPLES

57       Summarize block device I/O latency as a histogram:
58              # biolatency
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60       Print 1 second summaries, 10 times:
61              # biolatency 1 10
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63       Print  1  second  summaries,  using  milliseconds as units for the his‐
64       togram, and
65              include timestamps on output: # biolatency -mT 1
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67       Include OS queued time in I/O time:
68              # biolatency -Q
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70       Show a latency histogram for each disk device separately:
71              # biolatency -D
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73       Show a latency histogram in a dictionary format:
74              # biolatency -j
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76       Also show extension summary(total, average):
77              # biolatency -e
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FIELDS

80       usecs  Microsecond range
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82       msecs  Millisecond range
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84       count  How many I/O fell into this range
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86       distribution
87              An ASCII bar chart to visualize the distribution (count column)
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OVERHEAD

90       This traces kernel functions and maintains in-kernel timestamps  and  a
91       histogram,  which  are asynchronously copied to user-space. This method
92       is very efficient, and the overhead for most storage I/O rates  (<  10k
93       IOPS) should be negligible.  If you have a higher IOPS storage environ‐
94       ment, test and quantify the overhead before use.
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SOURCE

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

105       Linux
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STABILITY

108       Unstable - in development.
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AUTHOR

111       Brendan Gregg, Rocky Xing
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