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 (warning: 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 quantify 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)