|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 seconds.
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 efficiency.
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.
- Include timestamps on output.
- Output histogram in milliseconds.
- Print a histogram per disk device.
- Output interval, in seconds.
- Number of outputs.
- 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
- Microsecond range
- Millisecond range
- How many I/O fell into this range
- 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 storage environment, test and quantify the overhead before use.
SOURCE¶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.
STABILITY¶Unstable - in development.