Provided by: bpfcc-tools_0.18.0+ds-2_all
biolatency - Summarize block device I/O latency as a histogram.
biolatency [-h] [-F] [-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 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.
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. -F Print a histogram per set of I/O flags. -j Print a histogram dictionary interval Output interval, in seconds. count 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 Show a latency histogram in a dictionary format: # biolatency -j
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)
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.
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.
Unstable - in development.