bcc-funcinterval - Man Page

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 funclatency, we can profile specific functions to know how latency this function costs. However, sometimes performance drop is not about the  latency of function but the interval between function calls. funcinterval is born for this purpose.

This tool uses in-kernel eBPF maps for storing timestamps and the histogram, 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

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 measurable. 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)

Info

2020-05-27 USER COMMANDS