[ag-automation] [ANNOUNCEMENT] PREEMPT_RT Patch 2.6.26.8-rt16 is now our "Latest Stable"

[Carsten Emde]

Dear List Member,

We are glad to announce that the "Latest Stable" [1] version of
real-time mainline Linux (aka PREEMPT_RT) is now based on kernel version
2.6.26. We have successfully tested the kernel 2.6.26-8-rt16 in a wide
variety of kernel configurations and on many different platforms. We
gratefully acknowledge the efforts of the main developers Steven Rostedt
and Thomas Gleixner and of the numerous testers and bug reporters who
have helped to make this happen.

What is new in 2.6.26.8-rt16?
As always, the "Latest Stable" 2.6.26.8-rt16 has a large number of bugs
fixed, some of them being introduced since the release of the "Lastest
Stable" 2.6.24 real-time kernel, some of them newly discovered (and
backported to 2.6.24), and some of them even found in the original
mainline Linux kernel. One of the latter is the spurious occurrence of
bad page states that Peter Zijlstra fixed in mainline (for details see
[2]) after it was first discovered in a real-time kernel.

In addition to these maintenance fixes, Linux kernels based on 2.6.26
incorporate, among others, two new features that are especially
important for us: Device tree support and improved kernel cache
management of the video buffer.

Device tree
The device tree was inspired from the Open Firmware project and is a
(simple) flat data structure containing information about the devices of
a given computer board. The device tree source (DTS) is compiled using
the device tree compiler (DTC), and the resulting device tree binary
(DTB) is integrated into the boot image. The device tree facilitates
board configuration and is required for the merging of the two PPC
architecture implementations ppc and powerpc.

Improved kernel cache management of the video buffer
This improved kernel cache management makes it possible for the first
time to use hardware-accelerated graphics in a real-time system without
any side effects of graphics operations on the real-time capabilities of
the system. There is only a minor restriction: Some latencies in the
range of several milliseconds occur once when the graphics board is
initialized for the first time. Later on, switching to and from graphics
or even restarting the X server does not produce any more latencies.
Since the initialization of the graphics board can be done at boot time
before the real-time critical application is started, this restriction
is normally not significant.

BTW: The 2.6.24 -rt tree will be maintained for some time, and fixes
will be backported should it be necessary.


Best regards,

Carsten Emde.


[1] http://www.osadl.org/Latest-Stable.latest-stable-realtime-linux.0.html
[2] http://linux.derkeiler.com/Mailing-Lists/Kernel/2009-01/msg13546.html