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

NAME
     latency -- monitors scheduling and interrupt latency

SYNOPSIS
     latency [-rt] [-h] [-c code_file] [-l log_file] [-st threshold] [-it threshold] [-s sleep_in_usecs]
             [-d decrementer_in_usecs] [-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 overrides the default location of the system call code file,
             which is found in /usr/share/misc/trace.codes.

     -d decrementer_in_usecs
             Sets the decrementer, using a value expressed in microseconds.  On exit, the decrementer is set
             back to the system default value.

     -it threshold
             Set the interrupt latency threshold, expressed in microseconds.  If the latency exceeds this
             value, and a log file has been specified, 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 /mach_kernel.  This option allows you to specify an
             alternate booted kernel.

     -rt     Sets the real-time scheduling policy.  Default policy is timeshare.

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

     -s sleep_in_usecs
             Sets the timer, taking an argument expressed in microseconds.  The default timer is set to 1000
             microseconds.

     -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.

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

Mac OS X                                       March 28, 2000                                       Mac OS X