From: pmf Date: Tue, 3 Feb 2009 02:11:52 +0000 (+0000) Subject: ust.html: update by Michel Dagenais X-Git-Tag: v0.12.20~178 X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=baec4c72d0a0fcf6b2d110a07e8c0889bf78826e;p=lttv.git ust.html: update by Michel Dagenais git-svn-id: http://ltt.polymtl.ca/svn@3311 04897980-b3bd-0310-b5e0-8ef037075253 --- diff --git a/trunk/lttv/doc/developer/ust.html b/trunk/lttv/doc/developer/ust.html index c1cbeb2e..181408ac 100644 --- a/trunk/lttv/doc/developer/ust.html +++ b/trunk/lttv/doc/developer/ust.html @@ -1,49 +1,21 @@ - - - - LTTng User-space Tracing Design - - - -

LTTng User-space Tracing Design

- -

-A user-space application may contain static instrumentation, and be linked with -an associated runtime library, in order to produce an execution trace. User -space Tracepoints and Markers, analogous to Kernel Tracepoints and Markers, -define program locations and arguments provided. Probes may then be connected to -each Tracepoint and Marker before they are activated. The probes will typically -call LTTng user-space event writing functions. - -

-When the instrumented application starts, a pipe is opened to allow external -tracing control, asynchronous notification is requested when commands arrive in -the pipe, and a signal handler is installed for SIGIO (or a carefully chosen -chainable signal number). Every time such signal is received, the runtime -library checks for commands received on the external tracing control pipe. The -recognized commands are: + + + -

  • list the available Markers and Tracepoints; -
  • dynamically load a library (presumably containing probes to connect); -
  • connect a probe to a Tracepoint or Marker; -
  • activate a Tracepoint or Marker; -
  • initialize the tracing buffers; -
  • flush the tracing buffers; -
  • finalize the tracing buffers; -

    -The application may also spontaneously provide information to the pipe: + LTTng User-space Tracing Design + -

  • a buffer is full; -
  • new tracepoints or markers are appearing or disappearing, because modules are - dynamically loaded or unloaded; +

    LTTng User-space Tracing Design

    -In addition, the tracing control application should be notified when the -application exits (to save the content of buffers if the application is -crashing). Such notification may be obtained through utrace. -

    -This tracing scheme plans to use a direct function call to tracing into buffers +Earlier versions of LTTng contained simple, system call based, tracepoints and fast, +user-space buffered, tracepoints for user-space tracing. During the kernel inclusion phase +of LTTng, extensive rework and modularization of the kernel tracing portion was undertaken. +This phase is well under way and several portions have been included already in the mainline kernel. +The rework of the kernel tracing infrastructure will shortly thereafter be ported to fast user-space +tracing. +This fast user-space tracing scheme uses a direct function call to write events into buffers mapped in user-space. This should be an order of magnitude faster than the current Dtrace implementation (c.f. Dtrace information @@ -53,13 +25,88 @@ a function call vs the int3 approach is available at Markers vs int3 performance comparison (see "Conclusion"). +

    +Libmarkers will provide applications with user-space Markers and Tracepoints +declarations, such that programmers will be able to insert Markers and Tracepoints in their +libraries and applications. User-space Tracepoints and Markers, analogous to Kernel Tracepoints and Markers, +define program locations and arguments provided. Libmarkers will also +provide utility functions to enumerate, activate and deactivate tracepoints and markers in the +process, and to associate probes with any tracepoint or marker. +

    + + +

    +Libtracing will provide the infrastructure to allocate buffers, define event types, write event +metadata and data to the buffers, and get notification when buffers are full. The initial implementation +will simply use one set of buffers per process. Subsequent more optimized versions will allocate one +set of buffers per thread; one set of buffers per CPU would be desirable but user-space programs cannot check +or control CPU migration without resorting to more costly bus locking operations or system calls. The library +provides a generic probe for markers which, when connected, generates an event in the buffer each time the marker +is encountered. + +

    +

    +Finally, libtracingcontrol opens a connection allowing a separate process (e.g. LTTng daemon, Eclipse, GDB) to control the +tracing within the application. Through this connection, the remote process can: + +

    + +In the first version, libtracingcontrol will simply contain the basic functionality +required to generate a trace of the Markers encountered. Subsequent versions will interact with +other probing mechanisms like GDB Tracepoints, user-space SystemTap and those defined by virtual +machines (e.g. Java Virtual Machine, Python, Errlang...). +

    Tracing of Java application is planned to be done through a JNI interface. Linking standard low-level C tracing library to the application within a JNI adaptation class will be required to trace Java events. This has been prototyped in the past. The work is available -here +here for older LTTng versions. +

    +The principle of operation of libtracingcontrol is that +when the instrumented application starts, a pipe is opened to allow external +tracing control. Asynchronous notification is requested when commands arrive in +the pipe, and a signal handler is installed for SIGIO (or a carefully chosen +chainable signal number). Every time such signal is received, the runtime +library checks for commands received on the external tracing control pipe. +The application may also spontaneously provide information to the remote control process +through the pipe: + +

    +

    +In addition, the tracing control application should be notified when the +application exits (to save the content of buffers if the application is +crashing) or forks (to trace the child as well if needed). +Such notification may be obtained through utrace. + +

    +In summary, a user-space application linking with libmarkers may contain static +instrumentation, Tracepoints and Markers, just like the kernel with Kernel Markers and Tracepoints. +The application can exploit this instrumentation itself or link with libtracing and have tracing probes +connected to each Marker. Other instrumentation mechanisms, like the GCC instrument-function option, or hooks +inserted by a JIT compiler, can also use libtracing to define and write event to the trace buffers. +Finally, libtracingcontrol, analogous to GDB stubs, allows the remote control of the tracing by remote +monitoring or debugging frameworks. - - +