documentation update

[ust.git] / doc / man / ustctl.1.md

diff --git a/doc/man/ustctl.1.md b/doc/man/ustctl.1.md
index 12437c5191307f6f9531b4e7e0628573c8887ab2..d0ecb983d5380831ccefb5f176c4998ca9f9f68c 100644 (file)
--- a/doc/man/ustctl.1.md
+++ b/doc/man/ustctl.1.md
@@ -7,7 +7,7 @@ ustctl(1) -- a program to control the tracing of userspace applications
 
 ## DESCRIPTION
 
-`ustclt` is a program to control the tracing of userspace applications. It can
+`ustctl` is a program to control the tracing of userspace applications. It can
 list markers, start the tracing, stop the tracing, enable/disable markers, etc.
 
 ## OPTIONS
@@ -22,7 +22,7 @@ starting with two dashes(`-'). A summary of options is included below.
     Create trace.
 
   * `--alloc-trace`:
-    Alloc trace.
+    Allocate trace.
 
   * `--start-trace`:
     Start tracing.
@@ -34,16 +34,16 @@ starting with two dashes(`-'). A summary of options is included below.
     Destroy the trace.
 
   * `--set-subbuf-size` <CHANNEL>/<bytes>:
-    Set the size of subbuffers per channel.
+    Set the size of subbuffers in CHANNEL.
 
   * `--set-subbuf-num` <CHANNEL>:
-    Set the number of subbuffers per channel.
+    Set the number of subbuffers per buffer for CHANNEL. Must be a power of 2.
 
   * `--get-subbuf-size` <CHANNEL>:
-    Get the size of subbuffers per channel.
+    Print the size of subbuffers per buffer for CHANNEL.
 
   * `--get-subbuf-num` <CHANNEL>:
-    Get the number of subbuffers per channel.
+    Print the number of subbuffers per buffer for CHANNEL.
 
   * `--enable-marker` <CHANNEL>/<MARKER>:
     Enable a marker.
@@ -54,9 +54,64 @@ starting with two dashes(`-'). A summary of options is included below.
   * `--list-markers`:
     List the markers of the process, their state and format string.
 
+## LIFE CYCLE OF A TRACE
+
+Typically, the first step is to enable markers with `--enable-marker`. An
+enabled marker generates an event when the control flow passes over it
+(assuming the trace is recording). A disabled marker produces nothing. Enabling
+and disabling markers may however be done at any point, including while the
+trace is being recorded.
+
+In order to record events, a trace is first created with `--create-trace`. At
+this point, the subbuffer count and size may be changed with `--set-subbuf-num`
+and `--set-subbuf-size`.
+
+Afterward, the trace may be allocated with `--alloc-trace`. This allocates the
+buffers in memory, so once this is done, the subbuffer size and count can not
+be changed. Trace allocation also causes the daemon to connect to the trace
+buffers and wait for data to arrive. Explicit allocation is optional, as it is
+done automatically at trace start.
+
+The trace may then be started with `--start-trace`. This results in events
+being recorded in the buffer. The daemon automatically collects these events.
+
+The trace may be stopped with `--stop-trace`, either definitely after all the
+wanted information is collected, or temporarily, before being started again
+with `--start-trace`. This results in effectively "pausing" the recording.
+
+Finally, when `--destroy-trace` is used, the trace buffers are unallocated.
+However, the memory may not be effectively freed until the daemon finishes to
+collect them.
+
+## STRUCTURE OF A TRACE
+
+Each instrumentation point that is added in a program is associated to a
+channel.
+
+Trace events are put in buffers. There is one buffer per channel, per cpu.
+For example, on a system with 4 cores and tracing an application with 3
+channels, there will be 12 buffers in total. The content of each of these
+buffers is put in a distinct file in the trace directory. For example, the
+`metadata_2` file contains the data that was extracted from the buffer that
+contained the events from the metadata channel and having occurred on cpu 2.
+
+In memory, each buffer is divided in subbuffers. Subbuffers are equally-sized,
+contiguous parts of a buffer. The size of a buffer is equal to the number of
+subbuffers it contains times the size of each subbuffer. When a subbuffer is
+full, it is collected by the daemon while the others are filled. If, however,
+the buffer size is too small, buffer overflows may occur and result in event
+loss. By default, the number of subbuffers per buffer is 2. Subbuffer size
+for a given channel may be chosen with `--set-subbuf-size` while the subbuffer
+count is set with `--set-subbuf-num`.
+
+## SEE ALSO
+
+usttrace(1), ustd(1)
+
 ## AUTHOR
 
 `ustctl` was written by Pierre-Marc Fournier.
 
 This manual page was written by Jon Bernard &lt;jbernard@debian.org&gt;, for
-the Debian project (and may be used by others).
+the Debian project (and may be used by others). It was updated by Pierre-Marc
+Fournier.