Manual: biolatency.bt

biolatency.bt(8)				   System Manager's Manual				    biolatency.bt(8)

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 com‐
       mentary for this tool.

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

	      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)