biosnoop(8)

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)