NAME

       biolatency.bt - Block I/O latency as a histogram. Uses bpftrace/eBPF.

SYNOPSIS

       biolatency.bt

DESCRIPTION

       This  tool summarizes time (latency) spent in block device I/O (disk I/O) as a power-of-2 histogram. This
       allows the distribution to be studied, including modes and outliers. There are often two modes,  one  for
       device  cache  hits and one for cache misses, which can be shown by this tool. Latency outliers will also
       be shown.

       The original tool, which is retained as "biolatency-kp.bt", currently works by  dynamic  tracing  of  the
       blk_account*()  kernel  functions,  which  will  need updating to match any changes to these functions in
       future kernels versions.

       The updated version of the tool utilizes tracepoints instead of kprobes so that it can be compatible with
       a wide range of kernel versions.

       Since this uses BPF, only the root user can use this tool.

REQUIREMENTS

       CONFIG_BPF and bpftrace.

EXAMPLES

       Trace block device I/O (disk I/O), and print a latency histogram on Ctrl-C:
              # biolatency.bt

FIELDS

       1st, 2nd
              This is a range of latency, in microseconds (shown in "[...)" set notation).

       3rd    A column showing the count of operations in this range.

       4th    This is an ASCII histogram representing the count column.

OVERHEAD

       Since block device I/O usually has a relatively low frequency (< 10,000/s), the overhead for this tool is
       expected to be negligible. For high IOPS storage systems, test and quantify before use.

SOURCE

       This is from bpftrace.

              https://github.com/bpftrace/bpftrace

       Also look in the bpftrace distribution for a  companion  _examples.txt  file  containing  example  usage,
       output, and commentary for this tool.

       This  is  a  bpftrace version of the bcc tool of the same name. The bcc tool may provide more options and
       customizations.

              https://github.com/iovisor/bcc

OS

       Linux

STABILITY

       Unstable - in development.

AUTHOR

       Brendan Gregg

SEE ALSO

       biosnoop.bt(8)

USER COMMANDS                                      2018-09-13                                   biolatency.bt(8)