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.bt(8)