NAME

       biosnoop - Trace block device I/O and print details incl. issuing PID.

SYNOPSIS

       biosnoop [-hQ]

DESCRIPTION

       This  tools traces block device I/O (disk I/O), and prints a one-line summary for each I/O
       showing various details. These include the latency from the time of issue to the device to
       its  completion,  and  the PID and process name from when the I/O was first created (which
       usually identifies the responsible process).

       This uses in-kernel eBPF maps to cache process details (PID and comm) by I/O  request,  as
       well as a starting timestamp for calculating I/O latency.

       This  works  by  tracing  various kernel blk_*() functions using dynamic tracing, and will
       need updating to match any changes to these functions.

       This makes use of a Linux 4.4 feature (bpf_perf_event_output()); for  kernels  older  than
       4.4, see the version under tools/old, which uses an older mechanism

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

REQUIREMENTS

       CONFIG_BPF and bcc.

OPTIONS

       -h     Print usage message.

       -Q     Include a column showing the time spent quueued in the OS.

EXAMPLES

       Trace all block device I/O and print a summary line per I/O:
              # biosnoop

FIELDS

       TIME(s)
              Time of the I/O completion, in seconds since the first I/O was seen.

       COMM   Cached  process  name,  if present. This usually (but isn't guaranteed) to identify
              the responsible process for the I/O.

       PID    Cached process ID, if present. This usually (but isn't guaranteed) to identify  the
              responsible process for the I/O.

       DISK   Disk device name.

       T      Type of I/O: R = read, W = write. This is a simplification.

       SECTOR Device sector for the I/O.

       BYTES  Size of the I/O, in bytes.

       QUE(ms)
              Time  the  I/O  was  queued  in  the  OS  before  being  issued  to  the device, in
              milliseconds.

       LAT(ms)
              Time for the I/O (latency) from the issue to the  device,  to  its  completion,  in
              milliseconds.

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 bcc.

              https://github.com/iovisor/bcc

       Also  look  in  the bcc 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

       disksnoop(8), iostat(1)