latency man page on OpenDarwin

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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
	     overrides 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 argu‐
	     ment, 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 thresh‐
     old 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
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