1biolatency(8) System Manager's Manual biolatency(8)
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6 biolatency - Summarize block device I/O latency as a histogram.
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9 biolatency [-h] [-F] [-T] [-Q] [-m] [-D] [-e] [interval [count]]
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12 biolatency traces block device I/O (disk I/O), and records the distri‐
13 bution of I/O latency (time). This is printed as a histogram either on
14 Ctrl-C, or after a given interval in seconds.
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16 The latency of disk I/O operations is measured from when requests are
17 issued to the device up to completion. A -Q option can be used to in‐
18 clude time queued in the kernel.
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20 This tool uses in-kernel eBPF maps for storing timestamps and the his‐
21 togram, for efficiency.
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23 This works by tracing various kernel blk_*() functions using dynamic
24 tracing, and will need updating to match any changes to these func‐
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27 Since this uses BPF, only the root user can use this tool.
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30 CONFIG_BPF and bcc.
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33 -h Print usage message.
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35 -T Include timestamps on output.
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37 -m Output histogram in milliseconds.
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39 -D Print a histogram per disk device.
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41 -F Print a histogram per set of I/O flags.
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43 -j Print a histogram dictionary
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45 -e Show extension summary(total, average)
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47 interval
48 Output interval, in seconds.
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50 count Number of outputs.
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53 Summarize block device I/O latency as a histogram:
54 # biolatency
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56 Print 1 second summaries, 10 times:
57 # biolatency 1 10
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59 Print 1 second summaries, using milliseconds as units for the his‐
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61 include timestamps on output: # biolatency -mT 1
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63 Include OS queued time in I/O time:
64 # biolatency -Q
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66 Show a latency histogram for each disk device separately:
67 # biolatency -D
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69 Show a latency histogram in a dictionary format:
70 # biolatency -j
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72 Also show extension summary(total, average):
73 # biolatency -e
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76 usecs Microsecond range
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78 msecs Millisecond range
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80 count How many I/O fell into this range
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82 distribution
83 An ASCII bar chart to visualize the distribution (count column)
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86 This traces kernel functions and maintains in-kernel timestamps and a
87 histogram, which are asynchronously copied to user-space. This method
88 is very efficient, and the overhead for most storage I/O rates (< 10k
89 IOPS) should be negligible. If you have a higher IOPS storage environ‐
90 ment, test and quantify the overhead before use.
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93 This is from bcc.
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95 https://github.com/iovisor/bcc
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97 Also look in the bcc distribution for a companion _examples.txt file
98 containing example usage, output, and commentary for this tool.
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101 Linux
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104 Unstable - in development.
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107 Brendan Gregg
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110 biosnoop(8)
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114USER COMMANDS 2020-12-30 biolatency(8)