NAME

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

SYNOPSIS

       biosnoop

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 4.5 feature (bpf_perf_event_output()); for kernels older than 4.5, 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.

EXAMPLES

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

FIELDS

       TIME(s)
              Time of the I/O, 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.

       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)