timerate(3tcl) Tcl Built-In Commands timerate(3tcl)
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NAME
timerate - Calibrated performance measurements of script execution time
SYNOPSIS
timerate script ?time? ?max-count?
timerate ?-direct? ?-overhead double? script ?time? ?max-count?
timerate ?-calibrate? ?-direct? script ?time? ?max-count?
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DESCRIPTION
The timerate command does calibrated performance measurement of a Tcl
command or script, script. The script should be written so that it can
be executed multiple times during the performance measurement process.
Time is measured in elapsed time using the finest timer resolution as
possible, not CPU time; if script interacts with the OS, the cost of
that interaction is included. This command may be used to provide in-
formation as to how well a script or Tcl command is performing, and can
help determine bottlenecks and fine-tune application performance.
The first and second form will evaluate script until the interval time
given in milliseconds elapses, or for 1000 milliseconds (1 second) if
time is not specified.
The parameter max-count could additionally impose a further restriction
by the maximal number of iterations to evaluate the script. If max-
count is specified, the evalution will stop either this count of itera-
tions is reached or the time is exceeded.
It will then return a canonical tcl-list of the form:
0.095977 µs/# 52095836 # 10419167 #/sec 5000.000 net-ms
which indicates:
• the average amount of time required per iteration, in microseconds
([lindex $result 0])
• the count how many times it was executed ([lindex $result 2])
• the estimated rate per second ([lindex $result 4])
• the estimated real execution time without measurement overhead
([lindex $result 6])
The following options may be supplied to the timerate command:
-calibrate
To measure very fast scripts as exactly as possible, a calibra-
tion process may be required. The -calibrate option is used to
calibrate timerate itself, calculating the estimated overhead of
the given script as the default overhead for future invocations
of the timerate command. If the time parameter is not specified,
the calibrate procedure runs for up to 10 seconds.
Note that calibration is not thread safe in the current imple-
mentation.
-overhead double
The -overhead parameter supplies an estimate (in microseconds)
of the measurement overhead of each iteration of the tested
script. This quantity will be subtracted from the measured time
prior to reporting results. This can be useful for removing the
cost of interpreter state reset commands from the script being
measured.
-direct
The -direct option causes direct execution of the supplied
script, without compilation, in a manner similar to the time
command. It can be used to measure the cost of Tcl_EvalObjEx, of
the invocation of canonical lists, and of the uncompiled ver-
sions of bytecoded commands.
As opposed to the time commmand, which runs the tested script for a
fixed number of iterations, the timerate command runs it for a fixed
time. Additionally, the compiled variant of the script will be used
during the entire measurement, as if the script were part of a compiled
procedure, if the -direct option is not specified. The fixed time pe-
riod and possibility of compilation allow for more precise results and
prevent very long execution times by slow scripts, making it practical
for measuring scripts with highly uncertain execution times.
EXAMPLES
Estimate how fast it takes for a simple Tcl for loop (including opera-
tions on variable i) to count to ten:
# calibrate
timerate -calibrate {}
# measure
timerate { for {set i 0} {$i<10} {incr i} {} } 5000
Estimate how fast it takes for a simple Tcl for loop, ignoring the
overhead of the management of the variable that controls the loop:
# 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
Estimate the speed of calculating the hour of the day using clock for-
mat only, ignoring overhead of the portion of the script that prepares
the time for it to calculate:
# calibrate
timerate -calibrate {}
# estimate overhead
set tm 0
set ovh [lindex [timerate {
incr tm [expr {24*60*60}]
}] 0]
# measure using estimated overhead
set tm 0
timerate -overhead $ovh {
clock format $tm -format %H
incr tm [expr {24*60*60}]; # overhead for this is ignored
} 5000
SEE ALSO
time(3tcl)
KEYWORDS
performance measurement, script, time
Tcl timerate(3tcl)
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