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 h
  13 .Op Fl c Ar code_file
  14 .Op Fl l Ar log_file
  15 .Op Fl st Ar threshold
  16 .Op Fl it Ar threshold
  17 .Op Fl s Ar sleep_in_usecs
  18 .Op Fl d Ar decrementer_in_usecs
  19 .Op Fl n Ar kernel
  20 .Sh DESCRIPTION
  21 The
  22 .Nm latency
  23 utility provides scheduling and interrupt-latency statistics.
  24 Due to the kernel tracing facility it uses to operate,
  25 the command requires root privileges.
  26 .Pp
  27 The arguments are as follows:
  28 .Bl -tag -width Ds
  29 .\" ==========
  30 .It Fl c Ar code_file
  31 When the
  32 .Fl c
  33 option is specified, it takes a path to a code file
  34 that contains the mappings for the system calls.
  35 This option overrides the default location of the system call code file,
  36 which is found in /usr/share/misc/trace.codes.
  37 .\" ==========
  38 .It Fl d Ar decrementer_in_usecs
  39 Sets the decrementer, using a value expressed in microseconds.
  40 On exit, the decrementer is set back to the system default value.
  41 .\" ==========
  42 .It Fl it Ar threshold
  43 Set the interrupt latency threshold,
  44 expressed in microseconds.
  45 If the latency exceeds this value,
  46 and a log file has been specified,
  47 a record of what occurred during this time is recorded.
  48 .\" ==========
  49 .It Fl l Ar log_file
  50 Specifies a log file that is written to when
  51 either the interrupt or scheduling latency is exceeded.
  52 .\" ==========
  53 .It Fl n Ar kernel
  54 By default,
  55 .Nm latency
  56 acts on the default /mach_kernel.
  57 This option allows you to specify an alternate booted kernel.
  58 .\" ==========
  59 .It Fl rt
  60 Sets the real-time scheduling policy.
  61 Default policy is timeshare.
  62 .\" ==========
  63 .It Fl h
  64 Display high resolution interrupt latencies and write them to latencies.csv (truncate existing file) upon exit.
  65 .\" ==========
  66 .It Fl s Ar sleep_in_usecs
  67 Sets the timer, taking an argument expressed in microseconds.
  68 The default timer is set to 1000 microseconds.
  69 .\" ==========
  70 .It Fl st Ar threshold
  71 Set the scheduler latency threshold in microseconds.
  72 If latency exceeds this, and a log file has been specified,
  73 a record of what occurred during this time is recorded.
  74 .El
  75 .Pp
  76 The data columns displayed are as follows:
  77 .Bl -tag -width LAST_PATHNAME_WAITED_FOR
  78 .It SCHEDULER
  79 The number of context switches that fall within the described delay.
  80 .It INTERRUPTS
  81 The number of interrupts that fall within the described delay.
  82 .El
  83 .Pp
  84 The
  85 .Nm latency
  86 utility is also SIGWINCH savvy, so adjusting your window geometry will change
  87 the list of delay values displayed.
  88 .Sh SAMPLE USAGE
  89 .Pp
  90 latency -rt -st 20000 -it 1000 -l /var/tmp/latency.log
  91 .Pp
  92 The
  93 .Nm latency
  94 utility will set the realtime scheduling policy.
  95 The threshold for the scheduler is set to 20000 microseconds.
  96 The threshold for interrupts is set to 1000 microseconds.
  97 Latencies that exceed these thresholds will be logged in /var/tmp/latency.log.
  98 .Sh SEE ALSO
  99 .Xr fs_usage 1 ,
 100 .Xr sc_usage 1 ,
 101 .Xr top 1