bcc-funcinterval(8)

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

6       funcinterval - Time interval between the same function, tracepoint as a
7       histogram.
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SYNOPSIS

10       funcinterval [-h] [-p PID] [-i INTERVAL] [-d DURATION] [-T]  [-u]  [-m]
11       [-v] pattern
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DESCRIPTION

14       This tool times interval between the same function as a histogram.
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16       eBPF/bcc  is very suitable for platform performance tuning.  By funcla‐
17       tency, we can profile specific functions to know how latency this func‐
18       tion  costs.  However,  sometimes  performance  drop  is  not about the
19       latency of function but the interval between function  calls.   funcin‐
20       terval is born for this purpose.
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22       This  tool uses in-kernel eBPF maps for storing timestamps and the his‐
23       togram, for efficiency.
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25       WARNING: This uses dynamic tracing of (what can be many) functions,  an
26       activity that has had issues on some kernel versions (risk of panics or
27       freezes). Test, and know what you are doing, before use.
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29       Since this uses BPF, only the root user can use this tool.
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REQUIREMENTS

32       CONFIG_BPF and bcc.
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OPTIONS

35       pattern Function name.  -h Print usage message.
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37       -p PID Trace this process ID only.
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39       -i INTERVAL
40              Print output every interval seconds.
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42       -d DURATION
43              Total duration of trace, in seconds.
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45       -T     Include timestamps on output.
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47       -u     Output histogram in microseconds.
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49       -m     Output histogram in milliseconds.
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51       -v     Print the BPF program (for debugging purposes).
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EXAMPLES

54       Time the interval of do_sys_open() kernel function as a histogram:
55              # funcinterval do_sys_open
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57       Time the interval of xhci_ring_ep_doorbell(), in microseconds:
58              # funcinterval -u xhci_ring_ep_doorbell
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60       Time the interval of do_nanosleep(), in milliseconds
61              # funcinterval -m do_nanosleep
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63       Output every 5 seconds, with timestamps:
64              # funcinterval -mTi 5 vfs_read
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66       Time process 181 only:
67              # funcinterval -p 181 vfs_read
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69       Time the interval of mm_vmscan_direct_reclaim_begin tracepoint:
70              # funcinterval t:vmscan:mm_vmscan_direct_reclaim_begin
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FIELDS

73       necs   Nanosecond range
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75       usecs  Microsecond range
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77       msecs  Millisecond range
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79       count  How many calls fell into this range
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81       distribution
82              An ASCII bar chart to visualize the distribution (count column)
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OVERHEAD

85       This traces kernel functions and maintains in-kernel timestamps  and  a
86       histogram,  which  are  asynchronously copied to user-space. While this
87       method is very efficient, the rate of kernel functions can also be very
88       high  (>1M/sec),  at which point the overhead is expected to be measur‐
89       able. Measure in a test environment  and  understand  overheads  before
90       use. You can also use funccount to measure the rate of kernel functions
91       over a short duration, to set some expectations before use.
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SOURCE

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

102       Linux
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STABILITY

105       Unstable - in development.
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AUTHOR

108       Edward Wu
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