NAME

       filetop - File reads and writes by filename and process. Top for files.

SYNOPSIS

       filetop  [-h] [-a] [-C] [-r MAXROWS] [-s {reads,writes,rbytes,wbytes}] [-p PID] [interval]
       [count]

DESCRIPTION

       This is top for files.

       This traces file reads and writes, and  prints  a  per-file  summary  every  interval  (by
       default,  1  second).  By  default  the  summary  is sorted on the highest read throughput
       (Kbytes). Sorting order can be changed via -s option. By default only IO on regular  files
       is shown. The -a option will list all file types (sockets, FIFOs, etc).

       This uses in-kernel eBPF maps to store per process summaries for efficiency.

       This  script  works  by  tracing the __vfs_read() and __vfs_write() functions using kernel
       dynamic tracing, which instruments explicit read and write calls. If  files  are  read  or
       written  using  another  means  (eg, via mmap()), then they will not be visible using this
       tool. Also, this tool will need updating to match any code changes to those vfs functions.

       This should be useful  for  file  system  workload  characterization  when  analyzing  the
       performance of applications.

       Note that tracing VFS level reads and writes can be a frequent activity, and this tool can
       begin to cost measurable overhead at high I/O rates.

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

REQUIREMENTS

       CONFIG_BPF and bcc.

OPTIONS

       -a     Include non-regular file types (sockets, FIFOs, etc).

       -C     Don't clear the screen.

       -r MAXROWS
              Maximum number of rows to print. Default is 20.

       -s {reads,writes,rbytes,wbytes}
              Sort column. Default is rbytes (read throughput).

       -p PID Trace this PID only.

       interval
              Interval between updates, seconds.

       count  Number of interval summaries.

EXAMPLES

       Summarize block device I/O by process, 1 second screen refresh:
              # filetop

       Don't clear the screen, and top 8 rows only:
              # filetop -Cr 8

       5 second summaries, 10 times only:
              # filetop 5 10

FIELDS

       loadavg:
              The contents of /proc/loadavg

       PID    Process ID.

       COMM   Process name.

       READS  Count of reads during interval.

       WRITES Count of writes during interval.

       R_Kb   Total read Kbytes during interval.

       W_Kb   Total write Kbytes during interval.

       T      Type of file: R == regular, S == socket, O == other (pipe, etc).

       FILE   Filename.

OVERHEAD

       Depending  on  the  frequency  of  application  reads  and  writes,  overhead  can  become
       significant,  in the worst case slowing applications by over 50%. Hopefully for real world
       workloads the overhead is much less -- test before use. The reason for the  high  overhead
       is  that VFS reads and writes can be a frequent event, and despite the eBPF overhead being
       very small per event, if you multiply this small overhead by a million events per  second,
       it  becomes a million times worse. Literally. You can gauge the number of reads and writes
       using the vfsstat(8) tool, also from bcc.

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

INSPIRATION

       top(1) by William LeFebvre

SEE ALSO

       vfsstat(8), vfscount(8), fileslower(8)