NAME

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

SYNOPSIS

       biosnoop [-h] [-Q] [-d DISK] [-P]

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 queued in the OS.

       -d DISK
              Trace this disk only.

       -P     Display block I/O pattern (sequential or random).

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, Rocky Xing

SEE ALSO

       disksnoop(8), iostat(1)

USER COMMANDS                                      2015-09-16                                        biosnoop(8)