.TH filetop 8  "2016-02-08" "USER COMMANDS"
.SH NAME
filetop \- File reads and writes by filename and process. Top for files.
.SH SYNOPSIS
.B filetop [\-h] [\-C] [\-r MAXROWS] [\-s {reads,writes,rbytes,wbytes}] [\-p PID] [interval] [count]
.SH 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 (sokets,
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.
.SH REQUIREMENTS
CONFIG_BPF and bcc.
.SH OPTIONS
.TP
\-a
Include non-regular file types (sockets, FIFOs, etc).
.TP
\-C
Don't clear the screen.
.TP
\-r MAXROWS
Maximum number of rows to print. Default is 20.
.TP
\-s {reads,writes,rbytes,wbytes}
Sort column. Default is rbytes (read throughput).
.TP
\-p PID
Trace this PID only.
.TP
interval
Interval between updates, seconds.
.TP
count
Number of interval summaries.

.SH EXAMPLES
.TP
Summarize block device I/O by process, 1 second screen refresh:
#
.B filetop
.TP
Don't clear the screen, and top 8 rows only:
#
.B filetop -Cr 8
.TP
5 second summaries, 10 times only:
#
.B filetop 5 10
.SH FIELDS
.TP
loadavg:
The contents of /proc/loadavg
.TP
PID
Process ID.
.TP
COMM
Process name.
.TP
READS
Count of reads during interval.
.TP
WRITES
Count of writes during interval.
.TP
R_Kb
Total read Kbytes during interval.
.TP
W_Kb
Total write Kbytes during interval.
.TP
T
Type of file: R == regular, S == socket, O == other (pipe, etc).
.SH 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.
.SH SOURCE
This is from bcc.
.IP
https://github.com/iovisor/bcc
.PP
Also look in the bcc distribution for a companion _examples.txt file containing
example usage, output, and commentary for this tool.
.SH OS
Linux
.SH STABILITY
Unstable - in development.
.SH AUTHOR
Brendan Gregg
.SH INSPIRATION
top(1) by William LeFebvre
.SH SEE ALSO
vfsstat(8), vfscount(8), fileslower(8)