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	1	.\" Copyright (c) 2000, Apple Computer, Inc. All rights reserved.
	2	.\"
	3	.Dd March 28, 2000
	4	.Dt LATENCY 1
	5	.Os "Mac OS X"
	6	.Sh NAME
	7	.Nm latency
	8	.Nd monitors scheduling and interrupt latency
	9	.Sh SYNOPSIS
	10	.Nm latency
	11	.Op Fl rt
	12	.Op Fl c Ar codefile
	13	.Op Fl l Ar logfile
	14	.Op Fl st Ar threshold
	15	.Op Fl it Ar threshold
	16	.Op Fl s Ar sleep_in_usecs
	17	.Op Fl d Ar decrementer_in_usecs
	18	.Op Fl n Ar kernel
	19	.Sh DESCRIPTION
	20	The
	21	.Nm latency
	22	utility provides scheduling and interrupt latency statistics.
	23	It requires root privileges due to the kernel tracing facility it uses to
	24	operate.
	25	.Pp
	26	The arguments are as follows:
	27	.Bl -tag -width Ds
	28	.It Fl rt
	29	Set real time scheduling policy.
	30	Default policy is timeshare.
	31	.It Fl c
	32	When the
	33	.Fl c
	34	option is specified, it takes a path to a
	35	.Ar codefile
	36	that contains the mappings for the system calls.
	37	This option overrides the default location of the system call codefile which is
	38	found in /usr/share/misc/trace.codes.
	39	.It Fl l
	40	Specifies a
	41	.Ar logfile
	42	that is written to when either the interrupt or scheduling latency is exceeded.
	43	.It Fl st
	44	Set the scheduler latency threshold in microseconds.
	45	If latency exceeds this, and a logfile has been specified, a record of what
	46	occurred during this time is recorded.
	47	.It Fl it
	48	Set the interrupt latency threshold in microseconds.
	49	If latency exceeds this, and a logfile has been specified, a record of what
	50	occurred during this time is recorded.
	51	.It Fl s
	52	The
	53	.Fl s
	54	option sets the timer.
	55	It takes microseconds as an argument, the default timer is set to 1000
	56	microseconds.
	57	.It Fl d
	58	The
	59	.Fl d
	60	option sets the decrementer.
	61	It takes microseconds as an argument.
	62	The decrementer is set back to the system default on exit.
	63	.It Fl n
	64	By default,
	65	.Nm latency
	66	acts on the default /mach_kernel.
	67	This option allows you to specify an alternate booted kernel.
	68	.El
	69	.Pp
	70	The data columns displayed are as follows:
	71	.Bl -tag -width LAST_PATHNAME_WAITED_FOR -compact
	72	.Pp
	73	.It SCHEDULER
	74	The number of context switches that fall within the described delay.
	75	.It INTERRUPTS
	76	The number of interrupts that fall within the described delay.
	77	.El
	78	.Pp
	79	The
	80	.Nm latency
	81	utility is also SIGWINCH savvy, so adjusting your window geometry will change
	82	the list of delay values displayed.
	83	.Sh SAMPLE USAGE
	84	.Pp
	85	latency -rt -st 20000 -it 1000 -l /var/tmp/latency.log
	86	.Pp
	87	The
	88	.Nm latency
	89	utility will set the realtime scheduling policy.
	90	The threshold for the scheduler is set to 20000 microseconds.
	91	The threshold for interrupts is set to 1000 microseconds.
	92	Latencies that exceed these thresholds will be logged in /var/tmp/latency.log.
	93	.Sh SEE ALSO
	94	.Xr top 1 ,
	95	.Xr fs_usage 1 ,
	96	.Xr sc_usage 1