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>] [<ARGS>]...
   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 commands.
  20
  21 ## COMMANDS
  22
  23 `ustctl` accepts commands followed by arguments for each respective command.
  24 Most commands require the pid of the application being traced.
  25
  26   * `create-trace` <PID> <TRACE>:
  27     Create trace.
  28
  29   * `alloc-trace` <PID> <TRACE>:
  30     Allocate trace.
  31
  32   * `start-trace` <PID> <TRACE>:
  33     Start tracing.
  34
  35   * `stop-trace` <PID> <TRACE>:
  36     Stop tracing.
  37
  38   * `destroy-trace` <PID> <TRACE>:
  39     Destroy the trace.
  40
  41   * `set-subbuf-size`  <PID> <TRACE> <CHANNEL>/<bytes>:
  42     Set the size of subbuffers in CHANNEL.
  43
  44   * `set-subbuf-num`  <PID> <TRACE> <CHANNEL>/<nr>:
  45     Set the number of subbuffers per buffer for CHANNEL. Must be a power of 2.
  46
  47   * `set-sock-path` <PID> <SOCKPATH>:
  48     Set the path of the daemon socket.
  49
  50   * `get-subbuf-size` <PID> <TRACE> <CHANNEL>:
  51     Print the size of subbuffers per buffer for CHANNEL.
  52
  53   * `get-subbuf-num` <PID> <TRACE> <CHANNEL>:
  54     Print the number of subbuffers per buffer for CHANNEL.
  55
  56   * `get-sock-path` <PID>:
  57     Get the path of the daemon socket.
  58
  59   * `enable-marker` <PID> <TRACE> <CHANNEL>/<MARKER>:
  60     Enable a marker.
  61
  62   * `disable-marker` <PID> <TRACE> <CHANNEL>/<MARKER>:
  63     Disable a marker.
  64
  65   * `list-markers` <PID>:
  66     List the markers of the process, their state and format string.
  67
  68   * `force-subbuf-switch` <PID> <TRACE>:
  69     Force a subbuffer switch. This will flush all the data currently held.
  70
  71 ## LIFE CYCLE OF A TRACE
  72
  73 Typically, the first step is to enable markers with `enable-marker`. An
  74 enabled marker generates an event when the control flow passes over it
  75 (assuming the trace is recording). A disabled marker produces nothing. Enabling
  76 and disabling markers may however be done at any point, including while the
  77 trace is being recorded.
  78
  79 In order to record events, a trace is first created with `create-trace`. At
  80 this point, the subbuffer count and size may be changed with `set-subbuf-num`
  81 and `set-subbuf-size`.
  82
  83 Afterward, the trace may be allocated with `alloc-trace`. This allocates the
  84 buffers in memory, so once this is done, the subbuffer size and count can not
  85 be changed. Trace allocation also causes the daemon to connect to the trace
  86 buffers and wait for data to arrive. Explicit allocation is optional, as it is
  87 done automatically at trace start.
  88
  89 The trace may then be started with `start-trace`. This results in events
  90 being recorded in the buffer. The daemon automatically collects these events.
  91
  92 The trace may be stopped with `stop-trace`, either definitely after all the
  93 wanted information is collected, or temporarily, before being started again
  94 with `start-trace`. This results in effectively 'pausing' the recording.
  95 After using `stop-trace`, if a daemon is collecting the trace, it may not
  96 have flushed to the disk the full contents of the buffer yet.
  97
  98 Finally, when `destroy-trace` is used, the trace buffers are unallocated.
  99 However, the memory may not be effectively freed until the daemon finishes to
 100 collect them. When the trace is being collected by `ust-consumerd`, this command
 101 guarantees its full contents is flushed to the disk.
 102
 103 ## STRUCTURE OF A TRACE
 104
 105 Each instrumentation point that is added in a program is associated to a
 106 channel.
 107
 108 Trace events are put in buffers. There is one buffer per channel, per cpu.
 109 For example, on a system with 4 cores and tracing an application with 3
 110 channels, there will be 12 buffers in total. The content of each of these
 111 buffers is put in a distinct file in the trace directory. For example, the
 112 `metadata_2` file contains the data that was extracted from the buffer that
 113 contained the events from the metadata channel and having occurred on cpu 2.
 114
 115 In memory, each buffer is divided in subbuffers. Subbuffers are equally-sized,
 116 contiguous parts of a buffer. The size of a buffer is equal to the number of
 117 subbuffers it contains times the size of each subbuffer. When a subbuffer is
 118 full, it is collected by the daemon while the others are filled. If, however,
 119 the buffer size is too small, buffer overflows may occur and result in event
 120 loss. By default, the number of subbuffers per buffer is 2. Subbuffer size
 121 for a given channel may be chosen with `set-subbuf-size` while the subbuffer
 122 count is set with `set-subbuf-num`.
 123
 124 ## SEE ALSO
 125
 126 usttrace(1), ust-consumerd(1)
 127
 128 ## AUTHOR
 129
 130 `ustctl` was written by Pierre-Marc Fournier.
 131
 132 This manual page was written by Jon Bernard &lt;jbernard@debian.org&gt;, for
 133 the Debian project (and may be used by others). It was updated by Pierre-Marc
 134 Fournier.