| .TH biolatency 8 "2015-08-20" "USER COMMANDS" |
| .SH NAME |
| biolatency \- Summarize block device I/O latency as a histogram. |
| .SH SYNOPSIS |
| .B biolatency [\-h] [\-T] [\-Q] [\-m] [\-D] [interval [count]] |
| .SH 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. |
| .SH REQUIREMENTS |
| CONFIG_BPF and bcc. |
| .SH OPTIONS |
| \-h |
| Print usage message. |
| .TP |
| \-T |
| Include timestamps on output. |
| .TP |
| \-m |
| Output histogram in milliseconds. |
| .TP |
| \-D |
| Print a histogram per disk device. |
| .TP |
| interval |
| Output interval, in seconds. |
| .TP |
| count |
| Number of outputs. |
| .SH EXAMPLES |
| .TP |
| Summarize block device I/O latency as a histogram: |
| # |
| .B biolatency |
| .TP |
| Print 1 second summaries, 10 times: |
| # |
| .B biolatency 1 10 |
| .TP |
| Print 1 second summaries, using milliseconds as units for the histogram, and |
| include timestamps on output: |
| # |
| .B biolatency \-mT 1 |
| .TP |
| Include OS queued time in I/O time: |
| # |
| .B biolatency \-Q |
| .TP |
| Show a latency histogram for each disk device separately: |
| # |
| .B biolatency \-D |
| .SH FIELDS |
| .TP |
| usecs |
| Microsecond range |
| .TP |
| mecs |
| Millisecond range |
| .TP |
| count |
| How many I/O fell into this range |
| .TP |
| distribution |
| An ASCII bar chart to visualize the distribution (count column) |
| .SH 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. |
| .SH SOURCE |
| This is from bcc. |
| .IP |
| https://github.com/iovisor/bcc |
| .PP |
| Also look in the bcc distribution for a companion _examples.txt file containing |
| example usage, output, and commentary for this tool. |
| .SH OS |
| Linux |
| .SH STABILITY |
| Unstable - in development. |
| .SH AUTHOR |
| Brendan Gregg |
| .SH SEE ALSO |
| biosnoop(8) |