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/iovisor/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)