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 .Nm latency
  21 provides scheduling and interrupt latency statistics.
  22 .Pp
  23 The arguments are as follows:
  24 .Bl -tag -width Ds
  25 .It Fl rt
  26 Set real time scheduling policy. Default policy is timeshare.
  27 .It Fl c
  28 When the
  29 .Fl c
  30 option is specified, it takes a path to a
  31 .Ar codefile
  32 that
  33 contains the mappings for the system calls.  This option
  34 overrides the default location of the system call codefile
  35 which is found in /usr/share/misc/trace.codes.
  36 .It Fl l
  37 Specifies a
  38 .Ar logfile
  39 that is written to when either the interrupt or scheduling
  40 latency is exceeded.
  41 .It Fl st
  42 Set the scheduler latency threshold in microseconds.  If latency
  43 exceeds this, and a logfile has been specified, a record
  44 of what occurred during this time is recorded.
  45 .It Fl it
  46 Set the interrupt latency threshold in microseconds.  If latency
  47 exceeds this, and a logfile has been specified, a record
  48 of what occurred during this time is recorded.
  49 .It Fl s
  50 The
  51 .Fl s
  52 option sets the timer.  It takes microseconds as an argument,
  53 the default timer is set to 1000 microseconds.
  54 .It Fl d
  55 The
  56 .Fl d
  57 option sets the decrementer.  It takes microseconds as an argument.
  58 The decrementer is set back to the system default on exit.
  59 .It Fl n
  60 By default,
  61 .Nm latency
  62 acts on the default /mach_kernel.  This option
  63 allows you to specify an alternate booted kernel.
  64 .El
  65 .Pp
  66 The data columns displayed are as follows:
  67 .Bl -tag -width LAST_PATHNAME_WAITED_FOR -compact
  68 .Pp
  69 .It SCHEDULER
  70 The number of context switches that fall
  71 within the described delay.
  72 .It INTERRUPTS
  73 The number of interrupts that fall
  74 within the described delay.
  75 .El
  76 .Pp
  77 The
  78 .Nm latency
  79 command is also SIGWINCH savvy, so adjusting your window geometry will change
  80 the list of delay values displayed.
  81 .Sh SAMPLE USAGE
  82 .Pp
  83 latency -rt -st 20000 -it 1000 -l /var/tmp/latency.log
  84 .Pp
  85 .Nm latency
  86 will set the realtime scheduling policy.  The threshold for the scheduler is set to
  87 20000 microseconds.  The threshold for interrupts is set to 1000
  88 microseconds.  Latencies that exceed these thresholds will be logged
  89 in /var/tmp/latency.log.
  90 .Sh SEE ALSO
  91 .Xr top 1
  92 .Xr fs_usage 1
  93 .Xr sc_usage 1