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)

USER COMMANDS                                      2020-12-30                                      biolatency(8)