biolatency(8) System Manager's Manual biolatency(8)
biolatency - Summarize block device I/O latency as a histogram.
biolatency [-h] [-T] [-Q] [-m] [-D] [interval [count]]
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‐
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‐
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.
CONFIG_BPF and bcc.
-h Print usage message.
-T Include timestamps on output.
-m Output histogram in milliseconds.
-D Print a histogram per disk device.
Output interval, in seconds.
count Number of outputs.
Summarize block device I/O latency as a histogram:
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
usecs Microsecond range
msecs Millisecond range
count How many I/O fell into this range
An ASCII bar chart to visualize the distribution (count column)
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.
This is from bcc.
Also look in the bcc distribution for a companion _examples.txt file containing example
usage, output, and commentary for this tool.
Unstable - in development.
USER COMMANDS 2015-08-20 biolatency(8)