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)