[RELEASE] LTTng modules 2.8.0 (Linux kernel tracer)

[Mathieu Desnoyers]

Hi,

This official lttng modules 2.8.0 release announcement marks the end of the
release candidates part of our release cycle. After hammering out a few
issues during RC, we are now ready for the stable version.

The LTTng modules provide Linux kernel tracing capability to the LTTng
2.x tracer toolset.

The "Isseki Nicho" LTTng release name is a microbrew beer, following
our usual theme.

Its description:

The result of a collaboration between "Dieu du Ciel!" and Nagano-based
"Shiga Kogen", Isseki Nicho is a strong Imperial Dark Saison offering a
rich roasted malt flavor combined with a complex fruity finish typical
of Saison yeasts.

Here are the new major features included in this release:

--- Real-Time Contexts ---

The new "interruptible", "preemptible", "need_reschedule" and
Preempt-RT specific "migratable" contexts can be specified with the
lttng add-context command. It allows tracing those states for the
traced thread.


--- Built-in LTTng modules ---

It is now possible to build LTTng modules into your Linux kernel
image rather than having them as kernel modules. To do so, follow
this documentation:

https://github.com/lttng/lttng-modules/blob/master/README.md#kernel-built-in-support


--- Instrumentation updates ---

- The ARM64 architecture is now supported,
- x86 page faults are now available,
- x86 irq_vectors are now available,
- Supports all stable Linux kernels from 2.6.36 to 4.5, as well as currently
  maintained Preempt-RT kernels (4.4.4-rt11 4.1.19-rt22 4.0.8-rt6 3.18.28-rt28
  3.14.64-rt67 3.12.56-rt76 3.10.100-rt110 3.4.110-rt140 3.2.78-rt113).


--- Clock plugin support ---

A clock plugin modules can now be loaded to override the clock source used
by lttng-modules. It can be useful in combination with custom clock
source hardware.


--- Metadata Regeneration ---

A number of users have been using LTTng to trace embedded systems,
which often boot with an unset clock, before any NTP correction could
occur. Since the wall-time would be sampled before any NTP correction,
viewers would generally show traces as having been recorded at an
incorrect point in time.

This new command, lttng metadata regenerate, forces LTTng to resample
the current wall-time to determine an appropriate offset and
regenerate a trace's metadata.

For more information on this command and its limitations, please refer
to lttng-metadata(1).


--- Discarded Events and Lost Packets Statistics ---

This release adds discarded events and lost packets accounting which
allows the LTTng client to print a warning when the tracer was forced
to discard events or overwrite packets. The warnings take the
following form:
[warning] 1234 events discarded, please refer to the documentation on
channel configuration.
or
[warning] 1234 packets, please refer to the documentation on channel
configuration.

We have decided to add these warnings since a growing number of users
have been running analyses based on traces, the result of which may be
unreliable when events or packets are dropped.

A new packet sequence number was also added to the trace's packet
context. This allows viewers to indicate lost packets when the
"overwrite" mode is being used. See the LTTng documentation for a
detailed explanation of discard and overwrite modes.

https://lttng.org/docs/#doc-channel-overwrite-mode-vs-discard-mode

We will cover all of these new features in depth in an upcoming post
on the official LTTng blog at lttng.org/blog in time for the final
release. The official documentation will also be updated to reflect
the addition of these new features.

As always, please report any issue you may encounter to bugs.lttng.org
or on this mailing list.


Project website: http://lttng.org
Documentation: http://lttng.org/docs
Download link: http://lttng.org/download

Changelog:

2016-05-20 (Bike-to-Work Day) LTTng modules 2.8.0
        * Fix: ring buffer: honor switch parameter type in remote switch
        * Fix: only flush non-metadata channels
        * Fix: don't perform extra flush on metadata channel
        * Fix: flush empty packets on snapshot channel
        * Fix: do not generate packet at destroy after stop
        * Fix: compat ioctl for flush/get metadata version
        * Fix: ctf_string() should handle NULL pointers
        * Fix: portability: no arith on void pointer
        * Fix: add missing tests/Kbuild
        * Test clock override plugin
        * Fix: add modules target to base Makefile
        * Fix: make clean does not include dot-config
        * Fix: trigger build error if CONFIG_TRACEPOINTS is not set
        * Documentation: document that CONFIG_MODULES not required when builtin
        * Fix: mm_page_alloc_extfrag instrumentation for kernel 3.16.35
        * Fix: integer endianness metadata generation
        * Fix: endianness of integers received by filter

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com