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114 lines
3.1 KiB
114 lines
3.1 KiB
4 months ago
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.TH xfsslower 8 "2016-02-11" "USER COMMANDS"
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.SH NAME
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xfsslower \- Trace slow xfs file operations, with per-event details.
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.SH SYNOPSIS
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.B xfsslower [\-h] [\-j] [\-p PID] [min_ms]
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.SH DESCRIPTION
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This tool traces common XFS file operations: reads, writes, opens, and
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syncs. It measures the time spent in these operations, and prints details
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for each that exceeded a threshold.
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WARNING: See the OVERHEAD section.
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By default, a minimum millisecond threshold of 10 is used. If a threshold of 0
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is used, all events are printed (warning: verbose).
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Since this works by tracing the xfs_file_operations interface functions, it
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will need updating to match any changes to these functions.
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Since this uses BPF, only the root user can use this tool.
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.SH REQUIREMENTS
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CONFIG_BPF and bcc.
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.SH OPTIONS
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\-p PID
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Trace this PID only.
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.TP
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min_ms
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Minimum I/O latency (duration) to trace, in milliseconds. Default is 10 ms.
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.SH EXAMPLES
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.TP
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Trace synchronous file reads and writes slower than 10 ms:
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#
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.B xfsslower
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.TP
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Trace slower than 1 ms:
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#
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.B xfsslower 1
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.TP
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Trace slower than 1 ms, and output just the fields in parsable format (csv):
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#
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.B xfsslower \-j 1
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.TP
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Trace all file reads and writes (warning: the output will be verbose):
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#
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.B xfsslower 0
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.TP
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Trace slower than 1 ms, for PID 181 only:
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#
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.B xfsslower \-p 181 1
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.SH FIELDS
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.TP
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TIME(s)
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Time of I/O completion since the first I/O seen, in seconds.
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.TP
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COMM
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Process name.
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.TP
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PID
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Process ID.
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.TP
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T
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Type of operation. R == read, W == write, O == open, S == fsync.
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.TP
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OFF_KB
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File offset for the I/O, in Kbytes.
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.TP
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BYTES
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Size of I/O, in bytes.
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.TP
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LAT(ms)
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Latency (duration) of I/O, measured from when it was issued by VFS to the
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filesystem, to when it completed. This time is inclusive of block device I/O,
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file system CPU cycles, file system locks, run queue latency, etc. It's a more
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accurate measure of the latency suffered by applications performing file
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system I/O, than to measure this down at the block device interface.
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.TP
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FILENAME
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A cached kernel file name (comes from dentry->d_iname).
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.TP
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ENDTIME_us
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Completion timestamp, microseconds (\-j only).
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.TP
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OFFSET_b
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File offset, bytes (\-j only).
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.TP
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LATENCY_us
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Latency (duration) of the I/O, in microseconds (\-j only).
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.SH OVERHEAD
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This adds low-overhead instrumentation to these XFS operations,
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including reads and writes from the file system cache. Such reads and writes
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can be very frequent (depending on the workload; eg, 1M/sec), at which
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point the overhead of this tool (even if it prints no "slower" events) can
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begin to become significant. Measure and quantify before use. If this
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continues to be a problem, consider switching to a tool that prints in-kernel
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summaries only.
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.PP
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Note that the overhead of this tool should be less than fileslower(8), as
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this tool targets xfs functions only, and not all file read/write paths
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(which can include socket I/O).
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.SH SOURCE
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This is from bcc.
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.IP
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https://github.com/iovisor/bcc
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.PP
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Also look in the bcc distribution for a companion _examples.txt file containing
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example usage, output, and commentary for this tool.
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.SH OS
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Linux
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.SH STABILITY
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Unstable - in development.
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.SH AUTHOR
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Brendan Gregg
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.SH SEE ALSO
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biosnoop(8), funccount(8), fileslower(8)
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