Section 8 · System administration

bcc-biosnoop.8

Package: bcc-tools

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biosnoop

NAME
SYNOPSIS
DESCRIPTION
REQUIREMENTS
OPTIONS
EXAMPLES
FIELDS
OVERHEAD
SOURCE
OS
STABILITY
AUTHOR
SEE ALSO

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