latency.1   [plain text]


.\" Copyright (c) 2000, Apple Computer, Inc.  All rights reserved.
.\"
.Dd March 28, 2000
.Dt LATENCY 1
.Os "Mac OS X"
.Sh NAME
.Nm latency
.Nd monitors scheduling and interrupt latency
.Sh SYNOPSIS
.Nm latency
.Op Fl rt
.Op Fl c Ar codefile
.Op Fl l Ar logfile
.Op Fl st Ar threshold
.Op Fl it Ar threshold
.Op Fl s Ar sleep_in_usecs
.Op Fl d Ar decrementer_in_usecs
.Op Fl n Ar kernel
.Sh DESCRIPTION
The
.Nm latency
utility provides scheduling and interrupt latency statistics.
It requires root privileges due to the kernel tracing facility it uses to
operate.
.Pp
The arguments are as follows:
.Bl -tag -width Ds
.It Fl rt
Set real time scheduling policy.
Default policy is timeshare.
.It Fl c
When the
.Fl c
option is specified, it takes a path to a 
.Ar 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.
.It Fl l
Specifies a
.Ar logfile
that is written to when either the interrupt or scheduling latency is exceeded.
.It Fl 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 Fl 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.
.It Fl s
The
.Fl s
option sets the timer.
It takes microseconds as an argument, the default timer is set to 1000
microseconds.
.It Fl d
The
.Fl d
option sets the decrementer.
It takes microseconds as an argument.
The decrementer is set back to the system default on exit.
.It Fl n
By default,
.Nm latency
acts on the default /mach_kernel.
This option allows you to specify an alternate booted kernel.
.El
.Pp
The data columns displayed are as follows:
.Bl -tag -width LAST_PATHNAME_WAITED_FOR -compact
.Pp
.It SCHEDULER
The number of context switches that fall within the described delay.
.It INTERRUPTS
The number of interrupts that fall within the described delay.
.El
.Pp
The
.Nm latency
utility is also SIGWINCH savvy, so adjusting your window geometry will change
the list of delay values displayed.
.Sh SAMPLE USAGE
.Pp
latency -rt -st 20000 -it 1000 -l /var/tmp/latency.log
.Pp
The
.Nm 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.
.Sh SEE ALSO
.Xr top 1 ,
.Xr fs_usage 1 ,
.Xr sc_usage 1