Man page - biolatency-bpfcc(8)
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apt-get install bpfcc-tools
Manual
| biolatency(8) | System Manager's Manual | biolatency(8) |
NAME
biolatency - Summarize block device I/O latency as a histogram.
SYNOPSIS
biolatency [-h] [-F] [-T] [-Q] [-m] [-D] [-F] [-e] [-j] [-d DISK] [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 disk I/O operations is measured from when requests are issued to the device up to 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.
- -T
- Include timestamps on output.
- -m
- Output histogram in milliseconds.
- -D
- Print a histogram per disk device.
- -F
- Print a histogram per set of I/O flags.
- -j
- Print a histogram dictionary
- -e
- Show extension summary(total, average)
- -d DISK
- Trace this disk only
- 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
- Show a latency histogram in a dictionary format:
- # biolatency -j
- Also show extension summary(total, average):
- # biolatency -e
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 storage 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, Rocky Xing
SEE ALSO
biosnoop(8)
| 2020-12-30 | USER COMMANDS |