cpudist-bpfcc(8)

Usage

cpudist [-h] [-O] [-T] [-m] [-P] [-L] [-p PID] [-I] [-e] [interval] [count]

Overview

This measures the time a task spends on the CPU before being descheduled, and shows the times as a histogram. Tasks that spend a very short time on the CPU can be indicative of excessive context-switches and poor workload distribution, and possibly point to a shared source of contention that keeps tasks switching in and out as it becomes available (such as a mutex).

Similarly, the tool can also measure the time a task spends off-CPU before it is scheduled again. This can be helpful in identifying long blocking and I/O operations, or alternatively very short descheduling times due to short-lived locks or timers.

By default CPU idle time are excluded by simply excluding PID 0.

This tool uses in-kernel eBPF maps for storing timestamps and the histogram, for efficiency. Despite this, the overhead of this tool may become significant for some workloads: see the OVERHEAD section.

Since this uses BPF, only the root user can use this tool.

Requirements

CONFIG_BPF and bcc.

Options

-h: Print usage message.

-O: Measure off-CPU time instead of on-CPU time.

-T: Include timestamps on output.

-m: Output histogram in milliseconds.

-P: Print a histogram for each PID (tgid from the kernel's perspective).

-L: Print a histogram for each TID (pid from the kernel's perspective).

-p PID: Only show this PID (filtered in kernel for efficiency).

-I: Include CPU idle time (by default these are excluded).

-e: Show extension summary (average/total/count).

`interval`	Output interval, in seconds.
`count`	Number of outputs.

Examples

`Summarize task on-CPU time as a histogram:`	# `cpudist`
`Summarize task off-CPU time as a histogram:`	# cpudist -O
`Print 1 second summaries, 10 times:`	# cpudist 1 10
`Print 1 second summaries, using milliseconds as units for the histogram, and include timestamps on output:`	# cpudist -mT 1
`Trace PID 185 only, 1 second summaries:`	# cpudist -p 185 1
`Include CPU idle time:`	# cpudist -I
`Also show extension summary:`	# cpudist -e

Fields

`usecs`	Microsecond range
`msecs`	Millisecond range
`count`	How many times a task event fell into this range
`distribution`	An ASCII bar chart to visualize the distribution (count column)

Overhead

This traces scheduler tracepoints, which can become very frequent. While eBPF has very low overhead, and this tool uses in-kernel maps for efficiency, the frequency of scheduler events for some workloads may be high enough that the overhead of this tool becomes significant. Measure in a lab environment to quantify the overhead before use.

Source

This is from bcc.

: https://github.com/iovisor/bcc

Also look in the bcc distribution for a companion _example.txt file containing example usage, output, and commentary for this tool.

OS

Linux

Stability

Unstable - in development.

Releases

4 releases since Debian 10 (Buster); the text changed 1 time.

-I since Debian 12 (Bookworm); -e since Debian 12 (Bookworm).