07-16-2011
Determining typing latency
Hi all,
When I use an editor (vi) that is spawned in a remote server, visually I could see the latency between typing a character/word and being displayed on the terminal. I could see this visually but how do I get a metric on this or how to quantify this?
As expected, when I type in a editor spawned in my local desktop there is no latency / there is latency that I cannot observe optically (as you know it looks like almost the same event - therefore typing a character and the character to appear on the screen)
Any pointers on how to quantify the typing latency?
I tried with wpm (words per minute), sometimes since the latency is high I am not really convinced whether that is a right metric.
Pointers please. Thanks
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LEARN ABOUT OPENDARWIN
latency
LATENCY(1) BSD General Commands Manual LATENCY(1)
NAME
latency -- monitors scheduling and interrupt latency
SYNOPSIS
latency [-rt] [-c codefile] [-l logfile] [-st threshold] [-it threshold] [-s sleep_in_usecs] [-d decrementer_in_usecs] [-n kernel]
DESCRIPTION
The latency utility provides scheduling and interrupt latency statistics. It requires root privileges due to the kernel tracing facility it
uses to operate.
The arguments are as follows:
-rt Set real time scheduling policy. Default policy is timeshare.
-c When the -c option is specified, it takes a path to a codefile that contains the mappings for the system calls. This option over-
rides the default location of the system call codefile which is found in /usr/share/misc/trace.codes.
-l Specifies a logfile that is written to when either the interrupt or scheduling latency is exceeded.
-st Set the scheduler latency threshold in microseconds. If latency exceeds this, and a logfile has been specified, a record of what
occurred during this time is recorded.
-it Set the interrupt latency threshold in microseconds. If latency exceeds this, and a logfile has been specified, a record of what
occurred during this time is recorded.
-s The -s option sets the timer. It takes microseconds as an argument, the default timer is set to 1000 microseconds.
-d The -d option sets the decrementer. It takes microseconds as an argument. The decrementer is set back to the system default on
exit.
-n By default, latency acts on the default /mach_kernel. This option allows you to specify an alternate booted kernel.
The data columns displayed are as follows:
SCHEDULER The number of context switches that fall within the described delay.
INTERRUPTS The number of interrupts that fall within the described delay.
The latency utility is also SIGWINCH savvy, so adjusting your window geometry will change the list of delay values displayed.
SAMPLE USAGE
latency -rt -st 20000 -it 1000 -l /var/tmp/latency.log
The latency utility will set the realtime scheduling policy. The threshold for the scheduler is set to 20000 microseconds. The threshold
for interrupts is set to 1000 microseconds. Latencies that exceed these thresholds will be logged in /var/tmp/latency.log.
SEE ALSO
top(1), fs_usage(1), sc_usage(1)
Mac OS X March 28, 2000 Mac OS X