LATENCY(1)						    BSD General Commands Manual 						LATENCY(1)

NAME

     latency -- monitors scheduling and interrupt latency

SYNOPSIS

     latency [-p priority] [-h] [-m] [-st threshold] [-it threshold] [-c code_file] [-l log_file] [-R raw_file] [-n kernel]

DESCRIPTION

     The latency utility provides scheduling and interrupt-latency statistics.	Due to the kernel tracing facility it uses to operate, the command
     requires root privileges.

     The arguments are as follows:

     -c code_file
	     When the -c option is specified, it takes a path to a code file that contains the mappings for the system calls.  This option over-
	     rides the default location of the system call code file, which is found in /usr/share/misc/trace.codes.

     -h      Display high resolution interrupt latencies and write them to latencies.csv (truncate existing file) upon exit.

     -m      Display per-CPU interrupt latency statistics.

     -it threshold
	     Set the interrupt latency threshold, expressed in microseconds.  If the latency exceeds this value, and a log file has been speci-
	     fied, a record of what occurred during this time is recorded.

     -l log_file
	     Specifies a log file that is written to when either the interrupt or scheduling latency is exceeded.

     -n kernel
	     By default, latency acts on the default /System/Library/Kernels/kernel.development.  This option allows you to specify an alternate
	     booted kernel.

     -p priority
	     Specifies the priority level to observe scheduler latencies for.  The default is realtime ( 97 ). A range of priorities to monitor
	     can also be provided, for example 31-47 or 0-127

     -st threshold
	     Set the scheduler latency threshold in microseconds.  If latency exceeds this, and a log file has been specified, a record of what
	     occurred during this time is recorded.

     -R raw_file
	     Specifies a raw trace file to use as input.

     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 -p 97 -st 20000 -it 1000 -l /var/tmp/latency.log

     The latency utility will watch threads with priority 97 for scheduling latencies.	The threshold for the scheduler is set to 20000 microsec-
     onds.  The threshold for interrupts is set to 1000 microseconds.  Latencies that exceed these thresholds will be logged in
     /var/tmp/latency.log.

SEE ALSO

     fs_usage(1), sc_usage(1), top(1)

Mac OS X							  March 28, 2000							  Mac OS X