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 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.
CONFIG_BPF and bcc.
-h Print usage message.
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.
Also look in the bcc distribution for a companion _examples.txt file containing example usage, output, and commentary for this tool.
Linux
Unstable - in development.
Brendan Gregg
2015-08-20 | USER COMMANDS |