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 (warn‐
       ing: 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 applications performing file system I/O, than to mea‐
	      sure 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 sys‐
       tem cache will incur extra overhead while tracing. Such reads and writes can be very frequent (depending on the work‐
       load;  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  btrfs‐
       dist(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, output, 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)