SIMPLE SOLUTIONS

BIOLATENCY-BPFCC(8) - Linux man page online | Administration and privileged commands

Summarize block device I/O latency as a histogram.

Chapter
2015-08-20
biolatency(8) System Manager's Manual biolatency(8)

NAME

biolatency - Summarize block device I/O latency as a histogram.

SYNOPSIS

biolatency [-h] [-T] [-Q] [-m] [-D] [interval [count]]

DESCRIPTION

biolatency traces block device I/O (disk I/O), and records the distribution of I/O latency (time). This is printed as a histogram either on Ctrl-C, or after a given interval in sec‐ onds. The latency of the disk I/O is measured from the issue to the device to its completion. A -Q option can be used to include time queued in the kernel. This tool uses in-kernel eBPF maps for storing timestamps and the histogram, for effi‐ ciency. This works by tracing various kernel blk_*() functions using dynamic tracing, and will need updating to match any changes to these functions. Since this uses BPF, only the root user can use this tool.

REQUIREMENTS

CONFIG_BPF and bcc.

OPTIONS

-h Print usage message. -T Include timestamps on output. -m Output histogram in milliseconds. -D Print a histogram per disk device. interval Output interval, in seconds. count Number of outputs.

EXAMPLES

Summarize block device I/O latency as a histogram: # biolatency Print 1 second summaries, 10 times: # biolatency 1 10 Print 1 second summaries, using milliseconds as units for the histogram, and include timestamps on output: # biolatency -mT 1 Include OS queued time in I/O time: # biolatency -Q Show a latency histogram for each disk device separately: # biolatency -D

FIELDS

usecs Microsecond range msecs Millisecond range count How many I/O 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. This method is very efficient, and the overhead for most storage I/O rates (< 10k IOPS) should be negligible. If you have a higher IOPS stor‐ age environment, test and quantify the overhead 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

Brendan Gregg

SEE ALSO

biosnoop(8)
USER COMMANDS 2015-08-20 biolatency(8)
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