funcinterval(8) System Manager's Manual funcinterval(8)
NAME
funcinterval - Time interval between the same function, tracepoint as a
histogram.
SYNOPSIS
funcinterval [-h] [-p PID] [-i INTERVAL] [-d DURATION] [-T] [-u] [-m]
[-v] pattern
DESCRIPTION
This tool times interval between the same function as a histogram.
eBPF/bcc is very suitable for platform performance tuning. By funcla-
tency, we can profile specific functions to know how latency this func-
tion costs. However, sometimes performance drop is not about the la-
tency of function but the interval between function calls. funcinter-
val is born for this purpose.
This tool uses in-kernel eBPF maps for storing timestamps and the his-
togram, for efficiency.
WARNING: This uses dynamic tracing of (what can be many) functions, an
activity that has had issues on some kernel versions (risk of panics or
freezes). Test, and know what you are doing, before use.
Since this uses BPF, only the root user can use this tool.
REQUIREMENTS
CONFIG_BPF and bcc.
OPTIONS
pattern Function name. -h Print usage message.
-p PID Trace this process ID only.
-i INTERVAL
Print output every interval seconds.
-d DURATION
Total duration of trace, in seconds.
-T Include timestamps on output.
-u Output histogram in microseconds.
-m Output histogram in milliseconds.
-v Print the BPF program (for debugging purposes).
EXAMPLES
Time the interval of do_sys_open() kernel function as a histogram:
# funcinterval do_sys_open
Time the interval of xhci_ring_ep_doorbell(), in microseconds:
# funcinterval -u xhci_ring_ep_doorbell
Time the interval of do_nanosleep(), in milliseconds
# funcinterval -m do_nanosleep
Output every 5 seconds, with timestamps:
# funcinterval -mTi 5 vfs_read
Time process 181 only:
# funcinterval -p 181 vfs_read
Time the interval of mm_vmscan_direct_reclaim_begin tracepoint:
# funcinterval t:vmscan:mm_vmscan_direct_reclaim_begin
Time the interval of c:malloc used by top every 3 seconds:
# funcinterval -p `pidof -s top` -i 3 c:malloc
Time /usr/local/bin/python main function:
# funcinterval /usr/local/bin/python:main
FIELDS
necs Nanosecond range
usecs Microsecond range
msecs Millisecond range
count How many calls fell into this range
distribution
An ASCII bar chart to visualize the distribution (count column)
OVERHEAD
This traces kernel functions and maintains in-kernel timestamps and a
histogram, which are asynchronously copied to user-space. While this
method is very efficient, the rate of kernel functions can also be very
high (>1M/sec), at which point the overhead is expected to be measur-
able. Measure in a test environment and understand overheads before
use. You can also use funccount to measure the rate of kernel functions
over a short duration, to set some expectations before use.
SOURCE
This is from bcc.
https://github.com/iovisor/bcc
Also look in the bcc distribution for a companion _examples.txt file
containing example usage, output, and commentary for this tool.
OS
Linux
STABILITY
Unstable - in development.
AUTHOR
Edward Wu
SEE ALSO
funclatency(8) funccount(8)
USER COMMANDS 2020-05-27 funcinterval(8)
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