Manual: zfsslower-bpfcc

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

NAME
       zfsslower - Trace slow zfs file operations, with per-event details.

SYNOPSIS
       zfsslower [-h] [-j] [-p PID] [min_ms]

DESCRIPTION
       This tool traces common ZFS file operations: reads, writes, opens, and syncs. It measures the time spent in these op‐
       erations, 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).

       This  uses  kernel dynamic tracing of the ZPL interface (ZFS POSIX Layer), and will need updates to match any changes
       to this interface.

       This is intended to work with the ZFS on Linux project:
	      http://zfsonlinux.org

       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:
	      # zfsslower

       Trace slower than 1 ms:
	      # zfsslower 1

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

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

       Trace slower than 1 ms, for PID 181 only:
	      # zfsslower -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 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 these ZFS 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 over‐
       head 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 zfs 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
       biosnoop(8), funccount(8), fileslower(8)

USER COMMANDS						 2016-02-11						zfsslower(8)