'\"
'\" Copyright (c) 2005 Sergey Brester aka sebres.
'\"
'\" See the file "license.terms" for information on usage and redistribution
'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
'\"
.TH timerate n "" Tcl "Tcl Built-In Commands"
.so man.macros
.BS
'\" Note:  do not modify the .SH NAME line immediately below!
.SH NAME
timerate \- Time-related execution resp. performance measurement of a script
.SH SYNOPSIS
\fBtimerate \fIscript\fR \fI?time ?max-count??\fR
.sp
\fBtimerate \fI?-direct?\fR \fI?-overhead double?\fR \fIscript\fR \fI?time ?max-count??\fR
.sp
\fBtimerate \fI?-calibrate?\fR \fI?-direct?\fR \fIscript\fR \fI?time ?max-count??\fR
.BE
.SH DESCRIPTION
.PP
The first and second form will evaluate \fIscript\fR until the interval
\fItime\fR given in milliseconds elapses, or for 1000 milliseconds (1 second)
if \fItime\fR is not specified.
.sp
The parameter \fImax-count\fR could additionally impose a further restriction
by the maximal number of iterations to evaluate the script.
If \fImax-count\fR is specified, the evalution will stop either this count of
iterations is reached or the time is exceeded.
.sp
It will then return a canonical tcl-list of the form
.PP
.CS
\fB0.095977 \(mcs/# 52095836 # 10419167 #/sec 5000.000 nett-ms\fR
.CE
.PP
which indicates:
.IP \(bu
the average amount of time required per iteration, in microseconds (lindex $result 0)
.IP \(bu
the count how many times it was executed (lindex $result 2)
.IP \(bu
the estimated rate per second (lindex $result 4)
.IP \(bu
the estimated real execution time without measurement overhead (lindex $result 6)
.PP
Time is measured in elapsed time using the finest timer resolution as possible,
not CPU time.
This command may be used to provide information as to how well the script or a
tcl-command is performing and can help determine bottlenecks and fine-tune
application performance.
.TP
\fI-calibrate\fR
.
To measure very fast scripts as exact as posible the calibration process
may be required.

The \fI-calibrate\fR option is used to calibrate timerate, calculating the
estimated overhead of the given script as the default overhead for future 
invocations of the \fBtimerate\fR command. If the \fItime\fR parameter is not 
specified, the calibrate procedure runs for up to 10 seconds.
.TP
\fI-overhead double\fR
.
The \fI-overhead\fR parameter supplies an estimate (in microseconds) of the
measurement overhead of each iteration of the tested script. This quantity
will be subtracted from the measured time prior to reporting results.
.TP
\fI-direct\fR
.
The \fI-direct\fR option causes direct execution of the supplied script,
without compilation, in a manner similar to the \fBtime\fR command. It can be
used to measure the cost of \fBTcl_EvalObjEx\fR, of the invocation of canonical
lists, and of the uncompiled versions of bytecoded commands.
.PP
As opposed to the \fBtime\fR commmand, which runs the tested script for a fixed
number of iterations, the timerate command runs it for a fixed time.
Additionally, the compiled variant of the script will be used during the entire
measurement, as if the script were part of a compiled procedure, if the \fI-direct\fR
option is not specified. The fixed time period and possibility of compilation allow
for more precise results and prevent very long execution times by slow scripts, making
it practical for measuring scripts with highly uncertain execution times.

.SH EXAMPLE
Estimate how fast it takes for a simple Tcl \fBfor\fR loop (including
operations on variable \fIi\fR) to count to a ten:
.PP
.CS
# calibrate:
timerate -calibrate {}
# measure:
timerate { for {set i 0} {$i<10} {incr i} {} } 5000
.CE
.PP
Estimate how fast it takes for a simple Tcl \fBfor\fR loop, ignoring the
overhead for to perform ten iterations, ignoring the overhead of the management
of the variable that controls the loop:
.PP
.CS
# calibrate for overhead of variable operations:
set i 0; timerate -calibrate {expr {$i<10}; incr i} 1000
# measure:
timerate { for {set i 0} {$i<10} {incr i} {} } 5000
.CE
.PP
Estimate the speed of calculating the hour of the day using \fBclock format\fR only,
ignoring overhead of the portion of the script that prepares the time for it to
calculate:
.PP
.CS
# calibrate:
timerate -calibrate {}
# estimate overhead:
set tm 0
set ovh [lindex [timerate { incr tm [expr {24*60*60}] }] 0]
# measure using esimated overhead:
set tm 0
timerate -overhead $ovh {
    clock format $tm -format %H
    incr tm [expr {24*60*60}]; # overhead for this is ignored
} 5000
.CE
.SH "SEE ALSO"
time(n)
.SH KEYWORDS
script, timerate, time
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