NAME

       biostacks - Show disk I/O latency with initialization stacks. Uses bpftrace/eBPF.

SYNOPSIS

       biostacks

DESCRIPTION

       This  tool  shows disk I/O latency histograms for each block I/O initialization path. This
       can help reveal the reason for  different  latencies,  as  some  may  be  created  by  log
       flushing, others by application reads, etc.

       This   works   by  tracing  the  blk_account_io_start()  and  the  blk_start_request()  or
       blk_mq_start_request() functions using dynamic instrumentation.   Linux  5.0  removed  the
       classic I/O scheduler, so the blk_start_request() probe can be removed from the tool (just
       delete it). This tool may need other maintenance to keep working if these functions change
       in later kernels.

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

REQUIREMENTS

       CONFIG_BPF and bpftrace.

EXAMPLES

       Trace disk I/O latency with initialization stacks:
              # biostacks.bt

FIELDS

       0th    An initialization kernel stack trace (shown in "@[...]") is printed before each I/O
              histogram.

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

       3rd    A column showing the count of I/O in this range.

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

OVERHEAD

       The rate of biostacks should be low (bounded by device IOPS), such that  the  overhead  of
       this tool is expected to be negligible.

SOURCE

       This  tool  originated  from the book "BPF Performance Tools", published by Addison Wesley
       (2019):

              http://www.brendangregg.com/bpf-performance-tools-book.html

       See the book for more documentation on this tool.

       This version is in the bpftrace repository:

              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.

OS

       Linux

STABILITY

       Unstable - in development.

AUTHOR

       Brendan Gregg

SEE ALSO

       biosnoop(8)