latency.tproj/latency.1

   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