lttng lib: ring buffer remove duplicate null pointer

[lttng-modules.git] / TODO

Please contact Mathieu Desnoyers <mathieu.desnoyers@efficios.com> for
questions about this TODO list. The "Cleanup/Testing" section would be
good to go through before integration into mainline. The "Features"
section is a wish list of features to complete before releasing the
"LTTng 2.0" final version, but are not required to have LTTng working.
These features are mostly performance enhancements and instrumentation
enhancements.

TODO:

A) Cleanup/Testing

	1) Remove debugfs "lttng" file (keep only procfs "lttng" file).
	   The rationale for this is that this file is needed for
	   user-level tracing support (LTTng-UST 2.0) intended to be
	   used on production system, and therefore should be present as
	   part of a "usually mounted" filesystem rather than a debug
	   filesystem.

	2) Test lib ring buffer snapshot feature.
	   When working on the lttngtop project, Julien Desfossez
	   reported that he needed to push the consumer position
	   forward explicitely with lib_ring_buffer_put_next_subbuf.
	   This means that although the usual case of pairs of
	   lib_ring_buffer_get_next_subbuf/lib_ring_buffer_put_next_subbuf
	   work fine, there is probably a problem that needs to be
	   investigated in
	   lib_ring_buffer_get_subbuf/lib_ring_buffer_put_subbuf, which
	   depend on the producer to push the reader position.
	   Contact: Julien Desfossez <julien.desfossez@polymtl.ca>


B) Features

	1) Integration of the LTTng 0.x trace clocks into
	   LTTng 2.0.
	     Currently using mainline kernel monotonic clock. NMIs can
	     therefore not be traced, and this causes a significant
	     performance degradation compared to the LTTng 0.x trace
	     clocks. Imply the creation of drivers/staging/lttng/arch to
	     contain the arch-specific clock support files.
	     * Dependency: addition of clock descriptions to CTF.
	   See: http://git.lttng.org/?p=linux-2.6-lttng.git;a=summary
	        for the LTTng 0.x git tree.

	2) Port OMAP3 LTTng trace clocks to x86 to support systems
	   without constant TSC.
	    * Dependency: (B.1)
	   See: http://git.lttng.org/?p=linux-2.6-lttng.git;a=summary
	        for the LTTng 0.x git tree.

	3) Implement mmap operation on an anonymous file created by a
	   LTTNG_KERNEL_CLOCK ioctl to export data to export
	   synchronized kernel and user-level LTTng trace clocks:
	   with:
	      - shared per-cpu data,
	      - read seqlock.
	   The content exported by this shared memory area will be
	   arch-specific.
	   * Dependency: (B.1) && (B.2)
	   See: http://git.lttng.org/?p=linux-2.6-lttng.git;a=summary
	        for the LTTng 0.x git tree, which has vDSO support for
	        LTTng trace clock on the x86 architecture.

	3) Integrate the "statedump" module from LTTng 0.x into LTTng
	   2.0.
	     * Dependency: addition of "dynamic enumerations" type to CTF.
	   See: http://git.lttng.org/?p=lttng-modules.git;a=shortlog;h=refs/heads/v0.19-stable
	        ltt-statedump.c

	4) Generate system call TRACE_EVENT headers for all
	   architectures (currently done: x86 32/64).

	5) Define "unknown" system calls into instrumentation/syscalls
	   override files / or do SYSCALL_DEFINE improvements to
	   mainline kernel to allow automatic generation of these
	   missing system call descriptions.

	6) Create missing tracepoint event headers files into
	   instrumentation/events from headers located in
	   include/trace/events/. Choice: either do as currently done,
	   and copy those headers locally into the lttng driver and
	   perform the modifications locally, or push TRACE_EVENT API
	   modification into mainline headers, which would require
	   collaboration from Ftrace/Perf maintainers.

	7) Poll: implement a poll and/or epoll exclusive wakeup scheme,
	   which contradicts POSIX, but protect multiple consumer
	   threads from thundering herd effect.

	8) Re-integrate sample modules from libringbuffer into
	   lttng driver. Those modules can be used as example of how to
	   use libringbuffer in other contexts than LTTng, and are
	   useful to perform benchmarks of the ringbuffer library.
	   See: http://www.efficios.com/ringbuffer

	9) NOHZ support for lib ring buffer. NOHZ infrastructure in the
	   Linux kernel does not support notifiers chains, which does
	   not let LTTng play nicely with low power consumption setups
	   for flight recorder (overwrite mode) live traces. One way to
	   allow integration between NOHZ and LTTng would be to add
	   support for such notifiers into NOHZ kernel infrastructure.

	10) Turn drivers/staging/lttng/ltt-probes.c probe_list into a
	    hash table. Turns O(n^2) trace systems registration (cost
	    for n systems) into O(n). (O(1) per system)

	11) drivers/staging/lttng/probes/lttng-ftrace.c:
	    LTTng currently uses kretprobes for per-function tracing,
	    not the function tracer. So lttng-ftrace.c should be used
	    for "all" function tracing.

	12) drivers/staging/lttng/probes/lttng-types.c:
	    This is a currently unused placeholder to export entire C
	    type declarations into the trace metadata, e.g. for support
	    of describing the layout of structures/enumeration mapping
	    along with syscall entry events.  The design of this support
	    will likely change though, and become integrated with the
	    TRACE_EVENT support within lttng, by adding new macros, and
	    support for generation of metadata from these macros, to
	    allow description of those compound types/enumerations.

Please send patches
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>