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   * `--force-switch`:
  64     Force a subbuffer switch. This will flush all the data currently held.
  65
  66 ## LIFE CYCLE OF A TRACE
  67
  68 Typically, the first step is to enable markers with `--enable-marker`. An
  69 enabled marker generates an event when the control flow passes over it
  70 (assuming the trace is recording). A disabled marker produces nothing. Enabling
  71 and disabling markers may however be done at any point, including while the
  72 trace is being recorded.
  73
  74 In order to record events, a trace is first created with `--create-trace`. At
  75 this point, the subbuffer count and size may be changed with `--set-subbuf-num`
  76 and `--set-subbuf-size`.
  77
  78 Afterward, the trace may be allocated with `--alloc-trace`. This allocates the
  79 buffers in memory, so once this is done, the subbuffer size and count can not
  80 be changed. Trace allocation also causes the daemon to connect to the trace
  81 buffers and wait for data to arrive. Explicit allocation is optional, as it is
  82 done automatically at trace start.
  83
  84 The trace may then be started with `--start-trace`. This results in events
  85 being recorded in the buffer. The daemon automatically collects these events.
  86
  87 The trace may be stopped with `--stop-trace`, either definitely after all the
  88 wanted information is collected, or temporarily, before being started again
  89 with `--start-trace`. This results in effectively 'pausing' the recording.
  90 After using `--stop-trace`, if a daemon is collecting the trace, it may not
  91 have flushed to the disk the full contents of the buffer yet.
  92
  93 Finally, when `--destroy-trace` is used, the trace buffers are unallocated.
  94 However, the memory may not be effectively freed until the daemon finishes to
  95 collect them. When the trace is being collected by `ustd`, this command
  96 guarantees its full contents is flushed to the disk.
  97
  98 ## STRUCTURE OF A TRACE
  99
 100 Each instrumentation point that is added in a program is associated to a
 101 channel.
 102
 103 Trace events are put in buffers. There is one buffer per channel, per cpu.
 104 For example, on a system with 4 cores and tracing an application with 3
 105 channels, there will be 12 buffers in total. The content of each of these
 106 buffers is put in a distinct file in the trace directory. For example, the
 107 `metadata_2` file contains the data that was extracted from the buffer that
 108 contained the events from the metadata channel and having occurred on cpu 2.
 109
 110 In memory, each buffer is divided in subbuffers. Subbuffers are equally-sized,
 111 contiguous parts of a buffer. The size of a buffer is equal to the number of
 112 subbuffers it contains times the size of each subbuffer. When a subbuffer is
 113 full, it is collected by the daemon while the others are filled. If, however,
 114 the buffer size is too small, buffer overflows may occur and result in event
 115 loss. By default, the number of subbuffers per buffer is 2. Subbuffer size
 116 for a given channel may be chosen with `--set-subbuf-size` while the subbuffer
 117 count is set with `--set-subbuf-num`.
 118
 119 ## SEE ALSO
 120
 121 usttrace(1), ustd(1)
 122
 123 ## AUTHOR
 124
 125 `ustctl` was written by Pierre-Marc Fournier.
 126
 127 This manual page was written by Jon Bernard &lt;jbernard@debian.org&gt;, for
 128 the Debian project (and may be used by others). It was updated by Pierre-Marc
 129 Fournier.