Man page - f2fsslower-bpfcc(8)

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Package: bpfcc-tools
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bpfcc-tools

Manual

f2fsslower

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

NAME

f2fsslower - Trace slow f2fs file operations, with per-event details.

SYNOPSIS

f2fsslower [-h] [-s] [-p PID] [min_ms]

DESCRIPTION

This tool traces common f2fs file operations: reads, writes, opens, and syncs. It measures the time spent in these operations, and prints details for each that exceeded a threshold.

WARNING: See the OVERHEAD section.

By default, a minimum millisecond threshold of 10 is used. If a threshold of 0 is used, all events are printed (warning: verbose).

Since this works by tracing the f2fs_file_operations interface functions, it will need updating to match any changes to these functions.

Since this uses BPF, only the root user can use this tool.

REQUIREMENTS

CONFIG_BPF and bcc.

OPTIONS

-p PID Trace this PID only.

min_ms

Minimum I/O latency (duration) to trace, in milliseconds. Default is 10 ms.

EXAMPLES

Trace synchronous file reads and writes slower than 10 ms:

# f2fsslower

Trace slower than 1 ms:

# f2fsslower 1

Trace slower than 1 ms, and output just the fields in parsable format
(csv):

# f2fsslower -s 1

Trace all file reads and writes (warning: the output will be verbose):

# f2fsslower 0

Trace slower than 1 ms, for PID 181 only:

# f2fsslower -p 181 1

FIELDS

TIME(s)

Time of I/O completion since the first I/O seen, in seconds.

	COMM		Process name.
	PID		Process ID.
	T		Type of operation. R == read, W == write, O == open, S == fsync.
	OFF_KB		File offset for the I/O, in Kbytes.
	BYTES		Size of I/O, in bytes.

LAT(ms)

Latency (duration) of I/O, measured from when it was issued by VFS to the filesystem, to when it completed. This time is inclusive of block device I/O, file system CPU cycles, file system locks, run queue latency, etc. It’s a more accurate measure of the latency suffered by applications performing file system I/O, than to measure this down at the block device interface.

FILENAME

A cached kernel file name (comes from dentry->d_name.name).

ENDTIME_us

Completion timestamp, microseconds (-s only).

OFFSET_b

File offset, bytes (-s only).

LATENCY_us

Latency (duration) of the I/O, in microseconds (-s only).

OVERHEAD

This adds low-overhead instrumentation to these f2fs operations, including reads and writes from the file system cache. Such reads and writes can be very frequent (depending on the workload; eg, 1M/sec), at which point the overhead of this tool (even if it prints no "slower" events) can begin to become significant. Measure and quantify before use. If this continues to be a problem, consider switching to a tool that prints in-kernel summaries only.

Note that the overhead of this tool should be less than fileslower(8), as this tool targets f2fs functions only, and not all file read/write paths (which can include socket I/O).

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

Ting Zhang