Manual: btrfsslower-bpfcc

btrfsslower(8)				   System Manager's Manual			      btrfsslower(8)

NAME
       btrfsslower - Trace slow btrfs file operations, with per-event details.

SYNOPSIS
       btrfsslower [-h] [-j] [-p PID] [min_ms] [-d DURATION]

DESCRIPTION
       This  tool traces common btrfs 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 btrfs_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.

       -d DURATION
	      Total duration of trace in seconds.

EXAMPLES
       Trace synchronous file reads and writes slower than 10 ms:
	      # btrfsslower

       Trace slower than 1 ms:
	      # btrfsslower 1

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

       Trace all file reads and writes (warning: the output will be verbose):
	      # btrfsslower 0

       Trace slower than 1 ms, for PID 181 only:
	      # btrfsslower -p 181 1

       Trace for 10 seconds only:
	      # btrfsslower -d 10

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  appli‐
	      cations 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 (-j only).

       OFFSET_b
	      File offset, bytes (-j only).

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

OVERHEAD
       This  adds  low-overhead	 instrumentation to btrfs writes and fsyncs, as well as all system reads and
       opens (due to the current implementation of the btrfs_file_operations interface).  Particularly,	 all
       reads  and  writes from the file system cache will incur extra overhead while tracing. Such reads and
       writes can be very frequent (depending on the workload; eg, 1M/sec), at which point the	overhead  of
       this tool may become noticeable.	 Measure and quantify before use. If this continues to be a problem,
       consider switching to a tool that prints in-kernel summaries only, such as btrfsdist(8).

       Note  that  the	overhead  of this tool should be less than fileslower(8), as this tool targets btrfs
       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,	out‐
       put, and commentary for this tool.

OS
       Linux

STABILITY
       Unstable - in development.

AUTHOR
       Brendan Gregg

SEE ALSO
       btrfsdist(8), biosnoop(8), funccount(8), fileslower(8)

USER COMMANDS					 2016-02-15				      btrfsslower(8)