Manual: nfsslower-bpfcc

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

NAME
       nfsslower - Trace slow NFS file operations, with per-event details.

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

DESCRIPTION
       This tool traces common NFSv3 & NFSv4 file operations: reads, writes, opens, and getattrs. 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 nfs_file_operations interface functions, it will need updating to match any changes
       to these functions.

       This tool uses kprobes to instrument the kernel for entry and exit information, in the future a preferred  way  would
       be  to  use  tracepoints.   Currently  there  aren't  any tracepoints available for nfs_read_file, nfs_write_file and
       nfs_open_file, nfs_getattr does have entry and exit tracepoints but we chose to use kprobes for consistency

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

REQUIREMENTS
       CONFIG_BPF and bcc.

OPTIONS
       -p PID Trace this PID only.

       -j     Trace output in CSV format.

       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:
	      # nfsslower

       Trace slower than 1 ms:
	      # nfsslower 1

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

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

       Trace slower than 1 ms, for PID 181 only:
	      # nfsslower -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, G == getattr.

       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 RPC latency, network latency, cache lookup, remote fileserver processing latency,
	      etc.  Its a more accurate measure of the latency suffered by applications performing NFS read/write calls to a
	      fileserver.

       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 NFS operations, including reads and writes from the file system cache. Such
       read, writes and particularly getattrs 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 quan‐
       tify before use. If this continues to be a problem, consider switching to a  tool  that	prints	in-kernel  summaries
       only. This tool has been tested with NFSv3 & NVSv4, but it might work with NFSv{1,2}, since it is tracing the generic
       functions from nfs_file_operations.

       Note  that  the overhead of this tool should be less than fileslower(8), as this tool targets NFS functions only, and
       not all file read/write paths.

SOURCE
       This is from bcc.

	      https://github.com/iovisor/bcc

       Also look in the bcc distribution for a companion nfsslower_examples.txt file containing example usage,	output,	 and
       commentary for this tool.

OS
       Linux

STABILITY
       Unstable - in development.

AUTHOR
       Samuel Nair

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

USER COMMANDS						 2017-09-01						nfsslower(8)