doc/man/ustctl.1.md

   1 ustctl(1) -- a program to control the tracing of userspace applications
   2 =======================================================================
   3
   4 ## SYNOPSIS
   5
   6 `ustctl` [<command>] [<PIDs>]...
   7
   8 ## DESCRIPTION
   9
  10 `ustctl` is a program to control the tracing of userspace applications. It can
  11 list markers, start the tracing, stop the tracing, enable/disable markers, etc.
  12
  13 ## OPTIONS
  14
  15 These programs follow the usual GNU command line syntax, with long options
  16 starting with two dashes(`-'). A summary of options is included below.
  17
  18   * `-h`, `--help`:
  19     Show summary of options.
  20
  21   * `--create-trace`:
  22     Create trace.
  23
  24   * `--alloc-trace`:
  25     Allocate trace.
  26
  27   * `--start-trace`:
  28     Start tracing.
  29
  30   * `--stop-trace`:
  31     Stop tracing.
  32
  33   * `--destroy-trace`:
  34     Destroy the trace.
  35
  36   * `--set-subbuf-size` <CHANNEL>/<bytes>:
  37     Set the size of subbuffers in CHANNEL.
  38
  39   * `--set-subbuf-num` <CHANNEL>:
  40     Set the number of subbuffers per buffer for CHANNEL. Must be a power of 2.
  41
  42   * `--set-sock-path`:
  43     Set the path of the daemon socket.
  44
  45   * `--get-subbuf-size` <CHANNEL>:
  46     Print the size of subbuffers per buffer for CHANNEL.
  47
  48   * `--get-subbuf-num` <CHANNEL>:
  49     Print the number of subbuffers per buffer for CHANNEL.
  50
  51   * `--get-sock-path`:
  52     Get the path of the daemon socket.
  53
  54   * `--enable-marker` <CHANNEL>/<MARKER>:
  55     Enable a marker.
  56
  57   * `--disable-marker` <CHANNEL>/<MARKER>:
  58     Disable a marker.
  59
  60   * `--list-markers`:
  61     List the markers of the process, their state and format string.
  62
  63 ## LIFE CYCLE OF A TRACE
  64
  65 Typically, the first step is to enable markers with `--enable-marker`. An
  66 enabled marker generates an event when the control flow passes over it
  67 (assuming the trace is recording). A disabled marker produces nothing. Enabling
  68 and disabling markers may however be done at any point, including while the
  69 trace is being recorded.
  70
  71 In order to record events, a trace is first created with `--create-trace`. At
  72 this point, the subbuffer count and size may be changed with `--set-subbuf-num`
  73 and `--set-subbuf-size`.
  74
  75 Afterward, the trace may be allocated with `--alloc-trace`. This allocates the
  76 buffers in memory, so once this is done, the subbuffer size and count can not
  77 be changed. Trace allocation also causes the daemon to connect to the trace
  78 buffers and wait for data to arrive. Explicit allocation is optional, as it is
  79 done automatically at trace start.
  80
  81 The trace may then be started with `--start-trace`. This results in events
  82 being recorded in the buffer. The daemon automatically collects these events.
  83
  84 The trace may be stopped with `--stop-trace`, either definitely after all the
  85 wanted information is collected, or temporarily, before being started again
  86 with `--start-trace`. This results in effectively "pausing" the recording.
  87
  88 Finally, when `--destroy-trace` is used, the trace buffers are unallocated.
  89 However, the memory may not be effectively freed until the daemon finishes to
  90 collect them.
  91
  92 ## STRUCTURE OF A TRACE
  93
  94 Each instrumentation point that is added in a program is associated to a
  95 channel.
  96
  97 Trace events are put in buffers. There is one buffer per channel, per cpu.
  98 For example, on a system with 4 cores and tracing an application with 3
  99 channels, there will be 12 buffers in total. The content of each of these
 100 buffers is put in a distinct file in the trace directory. For example, the
 101 `metadata_2` file contains the data that was extracted from the buffer that
 102 contained the events from the metadata channel and having occurred on cpu 2.
 103
 104 In memory, each buffer is divided in subbuffers. Subbuffers are equally-sized,
 105 contiguous parts of a buffer. The size of a buffer is equal to the number of
 106 subbuffers it contains times the size of each subbuffer. When a subbuffer is
 107 full, it is collected by the daemon while the others are filled. If, however,
 108 the buffer size is too small, buffer overflows may occur and result in event
 109 loss. By default, the number of subbuffers per buffer is 2. Subbuffer size
 110 for a given channel may be chosen with `--set-subbuf-size` while the subbuffer
 111 count is set with `--set-subbuf-num`.
 112
 113 ## SEE ALSO
 114
 115 usttrace(1), ustd(1)
 116
 117 ## AUTHOR
 118
 119 `ustctl` was written by Pierre-Marc Fournier.
 120
 121 This manual page was written by Jon Bernard &lt;jbernard@debian.org&gt;, for
 122 the Debian project (and may be used by others). It was updated by Pierre-Marc
 123 Fournier.