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 p
  12 .Op Fl h
  13 .Op Fl m
  14 .Op Fl st Ar threshold
  15 .Op Fl it Ar threshold
  16 .Op Fl c Ar code_file
  17 .Op Fl l Ar log_file
  18 .Op Fl R Ar raw_file
  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 h
  39 Display high resolution interrupt latencies and write them to latencies.csv (truncate existing file) upon exit.
  40 .\" ==========
  41 .It Fl m
  42 Display per-CPU interrupt latency statistics.
  43 .\" ==========
  44 .It Fl it Ar threshold
  45 Set the interrupt latency threshold,
  46 expressed in microseconds.
  47 If the latency exceeds this value,
  48 and a log file has been specified,
  49 a record of what occurred during this time is recorded.
  50 .\" ==========
  51 .It Fl l Ar log_file
  52 Specifies a log file that is written to when
  53 either the interrupt or scheduling latency is exceeded.
  54 .\" ==========
  55 .It Fl n Ar kernel
  56 By default,
  57 .Nm latency
  58 acts on the default /mach_kernel.
  59 This option allows you to specify an alternate booted kernel.
  60 .\" ==========
  61 .It Fl p Ar priority
  62 Specifies the priority level to observe scheduler latencies for.
  63 .\" ==========
  64 .It Fl st Ar threshold
  65 Set the scheduler latency threshold in microseconds.
  66 If latency exceeds this, and a log file has been specified,
  67 a record of what occurred during this time is recorded.
  68 .\" ==========
  69 .It Fl R Ar raw_file
  70 Specifies a raw trace file to use as input.
  71 .El
  72 .Pp
  73 The data columns displayed are as follows:
  74 .Bl -tag -width LAST_PATHNAME_WAITED_FOR
  75 .It SCHEDULER
  76 The number of context switches that fall within the described delay.
  77 .It INTERRUPTS
  78 The number of interrupts that fall within the described delay.
  79 .El
  80 .Pp
  81 The
  82 .Nm latency
  83 utility is also SIGWINCH savvy, so adjusting your window geometry will change
  84 the list of delay values displayed.
  85 .Sh SAMPLE USAGE
  86 .Pp
  87 latency -p 97 -st 20000 -it 1000 -l /var/tmp/latency.log
  88 .Pp
  89 The
  90 .Nm latency
  91 utility will watch threads with priority 97 for scheduling latencies.
  92 The threshold for the scheduler is set to 20000 microseconds.
  93 The threshold for interrupts is set to 1000 microseconds.
  94 Latencies that exceed these thresholds will be logged in /var/tmp/latency.log.
  95 .Sh SEE ALSO
  96 .Xr fs_usage 1 ,
  97 .Xr sc_usage 1 ,
  98 .Xr top 1