Tag Archives: LTSI

AF_BUS, D-Bus, and the Linux kernel

By gregkh

nothing blocks

There’s been a lot of information scattered around the internet about
these topic recently, so here’s my attempt to put them all in one place
to (hopefully) settle things down and give my inbox a break.

Last week I spent a number of days at the GNOME Developer Hackfest
in Brussels, with the goal to help make the ability to distribute
applications written for GNOME (and even more generally, Linux) in a
better manner. A great summary of what happened there can be found in
this H-Online article. Also please read Alexander Larsson‘s
great summary of what we discussed
and worked on for another view of
this.

Both of these articles allude to the fact that I’m working on putting
the D-Bus protocol into the kernel, in order to help achieve these
larger goals of proper IPC for applications. And I’d like to confirm
that yes, this is true, but it’s not going to be D-Bus like you know it
today.

Our goal (and I use “goal” in a very rough term, I have 8 pages of
scribbled notes describing what we want to try to implement here), is to
provide a reliable multicast and point-to-point messaging system for the
kernel, that will work quickly and securely. On top of this kernel
feature, we will try to provide a “libdbus” interface that allows
existing D-Bus users to work without ever knowing the D-Bus daemon was
replaced on their system.

“But Greg!” some of you will shout, “What about the existing AF_BUS
kernel patches that have been floating around for a while and that you
put into the LTSI 3.4 kernel release?”

The existing AF_BUS patches are great for users who need a very
low-latency, high-speed, D-Bus protocol on their system. This includes
the crazy automotive Linux developers, who try to shove tens of
thousands of D-Bus messages through their system at boot time, all while
using extremely underpowered processors. For this reason, I included
the AF_BUS patches in the LTSI kernel release, as that limited
application can benefit from them.

Please remember the LTSI kernel is just like a distro kernel, it has no
relation to upstream kernel development other than being a consumer of
it. Patches are in this kernel because the LTSI member groups need
them, they aren’t always upstream, just like all Linux distro kernels
work.

However, given that the AF_BUS patches have been rejected by the
upstream Linux kernel developers, I advise that anyone relying on them
be very careful about their usage, and be prepared to move away from
them sometime in the future when this new “kernel dbus” code is properly
merged.

As for when this new kernel code will be finished, I can only respond
with the traditional “when it is done” mantra. I can’t provide any
deadlines, and at this point in time, don’t need any additional help
with it, we have enough people working on it at the moment. It’s
available publicly if you really …read more
Source: FULL ARTICLE at Linux Foundation

LTSI v3.4 Released

By Noriaki

Part of supporting the demand for Linux in consumer electronics is ensuring there is a common Linux base that is maintained and supported for the typical lifetime of a consumer device, usually two years, and that supports a large variety of consumer electronics products. The Linux kernel is released at such a rapid pace that until now, device makers were doing significant back-porting, bug testing and driver development on their own, which carried substantial cost in terms of time-to-market, as well as development and engineering effort to maintain those custom kernels.

The Linux Foundation’s Consumer Electronics (CE) workgroup founded the Long Term Support Initiative (LTSI) to address this issue collaboratively. Today, the project provides for both an annual release of a Linux kernel suitable for supporting the lifespan of consumer electronics products and regular updates of those releases for two years. Linux kernel maintainer Greg Kroah-Hartman oversees this maintenance and the LTSI kernel tree for this industry-wide project created and supported by Hitachi, LG Electronics, NEC, Panasonic, Qualcomm Atheros, Renesas Electronics Corporation, Samsung Electronics, Sony and Toshiba.

This week the CE working group is releasing the LTSI 3.4 kernel. It is based on the Linux 3.4.25 kernel release and includes a number of backported features from newer releases.

Highlights from today’s release include:

* The Contiguous Memory Allocator (CMA), which is extremely useful for embedded devices that have very limited hardware resources and will better handle the large memory requirements of multimedia applications. CMA originally was merged into the 3.4.0 kernel release, but its functionality was quite limited. Since then, the feature has been significantly improved in the kernel.org releases and those fixes have been added to the LTSI 3.4 kernel release. For more information about this kernel option, please visit LWN.net.

* AF_BUS, a kernel-based implementation of the D-Bus protocol. This feature was created for systems that required a faster D-Bus speed than the existing userspace method could provide, specifically the automotive entertainment systems. For more information about this feature, please see LWN.net.

* CoDel (controlled delay), a transmission algorithm that optimizes TCP/IP network buffer control, is backported for LTSI 3.4. This is a feature used to help control the “buffer bloat” problem that has been identified by the networking community as an issue that all devices need to be aware of. This feature was backported from the 3.5.0 kernel.org release. For more information about it, please see this LWN.net post.

Platform specific board support was backported from newer kernel versions, allowing the Armadillo 800, AT91, kzm9d, kzm9g, and Marzen platforms to work properly with this release.

For more information about LTSI and the latest release, please visit the LTSI website.

Source: FULL ARTICLE at Linux Foundation