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Measuring Program Resource Use: Top
Measuring Program Resource Use
1. Measuring Program Resource Use
The time command runs another program, then displays information
about the resources used by that program, collected by the system while
the program was running. You can select which information is reported
and the format in which it is shown (see section Setting the Output Format), or have
time save the information in a file instead of displaying it on the
screen (see section Redirecting Output).
The resources that time can report on fall into the general
categories of time, memory, and I/O and IPC calls. Some systems do not
provide much information about program resource use; time
reports unavailable information as zero values (see section Accuracy).
The format of the time command is:
| | time [option…] command [arg…]
|
time runs the program command, with any given arguments
arg…. When command finishes, time displays
information about resources used by command.
Here is an example of using time to measure the time and other
resources used by running the program grep:
| | eg$ time grep nobody /etc/aliases
nobody:/dev/null
etc-files:nobody
misc-group:nobody
0.07user 0.50system 0:06.69elapsed 8%CPU (0avgtext+489avgdata 324maxresident)k
46inputs+7outputs (43major+251minor)pagefaults 0swaps
|
Mail suggestions and bug reports for GNU time to
bug-gnu-utils@prep.ai.mit.edu. Please include the version of
time, which you can get by running `time --version', and the
operating system and C compiler you used.
1.1 Setting the Output Format
time uses a format string to determine which information to
display about the resources used by the command it runs. See section The Format String, for the interpretation of the format string contents.
You can specify a format string with the command line options listed
below. If no format is specified on the command line, but the
TIME environment variable is set, its value is used as the format
string. Otherwise, the default format built into time is used:
| | %Uuser %Ssystem %Eelapsed %PCPU (%Xtext+%Ddata %Mmax)k
%Iinputs+%Ooutputs (%Fmajor+%Rminor)pagefaults %Wswaps
|
The command line options to set the format are:
-
-f format
-
--format=format
Use format as the format string.
-
-p
-
--portability
Use the following format string, for conformance with POSIX standard
1003.2:
-
-q
-
--quiet
Suppress non-zero error code from the executed program.
-
-v
-
--verbose
-
Use the built-in verbose format, which displays each available piece of
information on the program's resource use on its own line, with an
English description of its meaning.
1.2 The Format String
The format string controls the contents of the time output.
It consists of resource specifiers and escapes, interspersed
with plain text.
A backslash introduces an escape, which is translated
into a single printing character upon output. The valid escapes are
listed below. An invalid escape is output as a question mark followed
by a backslash.
-
\t
a tab character
-
\n
a newline
-
\\
a literal backslash
time always prints a newline after printing the resource use
information, so normally format strings do not end with a newline
character (or `\n').
A resource specifier consists of a percent sign followed by another
character. An invalid resource specifier is output as a question mark
followed by the invalid character. Use `%%' to output a literal
percent sign.
The resource specifiers, which are a superset of those recognized by the
tcsh builtin time command, are listed below. Not all
resources are measured by all versions of Unix, so some of the values
might be reported as zero (see section Accuracy).
1.2.1 Time Resources
-
E
Elapsed real (wall clock) time used by the process, in
[hours:]minutes:seconds.
-
e
Elapsed real (wall clock) time used by the process, in
seconds.
-
S
Total number of CPU-seconds used by the system on behalf of the process
(in kernel mode), in seconds.
-
U
Total number of CPU-seconds that the process used directly (in user
mode), in seconds.
-
P
Percentage of the CPU that this job got. This is just user + system
times divied by the total running time.
1.2.2 Memory Resources
-
M
Maximum resident set size of the process during its lifetime, in
Kilobytes.
-
t
Average resident set size of the process, in Kilobytes.
-
K
Average total (data+stack+text) memory use of the process, in Kilobytes.
-
D
Average size of the process's unshared data area, in Kilobytes.
-
p
Average size of the process's unshared stack, in Kilobytes.
-
X
Average size of the process's shared text, in Kilobytes.
-
Z
System's page size, in bytes. This is a per-system constant, but
varies between systems.
1.2.3 I/O Resources
-
F
Number of major, or I/O-requiring, page faults that occurred while the
process was running. These are faults where the page has actually
migrated out of primary memory.
-
R
Number of minor, or recoverable, page faults. These are pages that are
not valid (so they fault) but which have not yet been claimed by other
virtual pages. Thus the data in the page is still valid but the system
tables must be updated.
-
W
Number of times the process was swapped out of main memory.
-
c
Number of times the process was context-switched involuntarily (because
the time slice expired).
-
w
Number of times that the program was context-switched voluntarily, for
instance while waiting for an I/O operation to complete.
-
I
Number of file system inputs by the process.
-
O
Number of file system outputs by the process.
-
r
Number of socket messages received by the process.
-
s
Number of socket messages sent by the process.
-
k
Number of signals delivered to the process.
1.2.4 Command Info
-
C
Name and command line arguments of the command being timed.
-
x
Exit status of the command.
1.3 Redirecting Output
By default, time writes the resource use statistics to the
standard error stream. The options below make it write the statistics
to a file instead. Doing this can be useful if the program you're
running writes to the standard error or you're running time
noninteractively or in the background.
-
-o file
-
--output=file
Write the resource use statistics to file. By default, this
overwrites the file, destroying the file's previous contents.
-
-a
-
--append
Append the resource use information to the output file instead
of overwriting it. This option is only useful with the `-o' or
`--output' option.
1.4 Examples
Run the command `wc /etc/hosts' and show the default information:
| | eg$ time wc /etc/hosts
35 111 1134 /etc/hosts
0.00user 0.01system 0:00.04elapsed 25%CPU (0avgtext+0avgdata 0maxresident)k
1inputs+1outputs (0major+0minor)pagefaults 0swaps
|
Run the command `ls -Fs' and show just the user, system, and
wall-clock time:
| | eg$ time -f "\t%E real,\t%U user,\t%S sys" ls -Fs
total 16
1 account/ 1 db/ 1 mail/ 1 run/
1 backups/ 1 emacs/ 1 msgs/ 1 rwho/
1 crash/ 1 games/ 1 preserve/ 1 spool/
1 cron/ 1 log/ 1 quotas/ 1 tmp/
0:00.03 real, 0.00 user, 0.01 sys
|
Edit the file `.bashrc' and have time append the elapsed time
and number of signals to the file `log', reading the format string
from the environment variable TIME:
| | eg$ export TIME="\t%E,\t%k" # If using bash or ksh
eg$ setenv TIME "\t%E,\t%k" # If using csh or tcsh
eg$ time -a -o log emacs .bashrc
eg$ cat log
0:16.55, 726
|
Run the command `sleep 4' and show all of the information about it
verbosely:
| | eg$ time -v sleep 4
Command being timed: "sleep 4"
User time (seconds): 0.00
System time (seconds): 0.05
Percent of CPU this job got: 1%
Elapsed (wall clock) time (h:mm:ss or m:ss): 0:04.26
Average shared text size (kbytes): 36
Average unshared data size (kbytes): 24
Average stack size (kbytes): 0
Average total size (kbytes): 60
Maximum resident set size (kbytes): 32
Average resident set size (kbytes): 24
Major (requiring I/O) page faults: 3
Minor (reclaiming a frame) page faults: 0
Voluntary context switches: 11
Involuntary context switches: 0
Swaps: 0
File system inputs: 3
File system outputs: 1
Socket messages sent: 0
Socket messages received: 0
Signals delivered: 1
Page size (bytes): 4096
Exit status: 0
|
1.5 Accuracy
The elapsed time is not collected atomically with the execution of the
program; as a result, in bizarre circumstances (if the time
command gets stopped or swapped out in between when the program being
timed exits and when time calculates how long it took to run), it
could be much larger than the actual execution time.
When the running time of a command is very nearly zero, some values
(e.g., the percentage of CPU used) may be reported as either zero (which
is wrong) or a question mark.
Most information shown by time is derived from the wait3
system call. The numbers are only as good as those returned by
wait3. Many systems do not measure all of the resources that
time can report on; those resources are reported as zero. The
systems that measure most or all of the resources are based on 4.2 or
4.3BSD. Later BSD releases use different memory management code that
measures fewer resources.
On systems that do not have a wait3 call that returns status
information, the times system call is used instead. It provides
much less information than wait3, so on those systems time
reports most of the resources as zero.
The `%I' and `%O' values are allegedly only "real" input
and output and do not include those supplied by caching devices. The
meaning of "real" I/O reported by `%I' and `%O' may be
muddled for workstations, especially diskless ones.
1.6 Running the time Command
The format of the time command is:
| | time [option…] command [arg…]
|
time runs the program command, with any given arguments
arg…. When command finishes, time displays
information about resources used by command (on the standard error
output, by default). If command exits with non-zero status or is
terminated by a signal, time displays a warning message and the
exit status or signal number.
Options to time must appear on the command line before
command. Anything on the command line after command is
passed as arguments to command.
-
-o file
-
--output=file
Write the resource use statistics to file.
-
-a
-
--append
Append the resource use information to the output file instead
of overwriting it.
-
-f format
-
--format=format
Use format as the format string.
-
--help
Print a summary of the command line options to time and exit.
-
-p
-
--portability
Use the POSIX format.
-
-v
-
--verbose
-
Use the built-in verbose format.
-
-V
-
--version
-
Print the version number of time and exit.
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