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Linux Kernel 2.4 Or 2.6 In Embedded System?
snikulin writes "My 6-year-old embedded software happily runs on kernel v2.4 on an XScale CPU. The software gets a bunch (tens of megabytes) of data from an FPGA over a PCI-X bus and pushes it out over GigE to data-processing equipment. The tool chain is based on the somewhat outdated gcc v2.95. Now, for certain technical reasons we want to jump from the ARM-based custom board to an Atom-based COM Express module. This implies that I'll need to re-create a Linux RAM disk from scratch along with the tool chain. The functionality of the software will be essentially the same. My question: is it worth it to jump to kernel 2.6, or better to stick with the old and proven 2.4? What will I gain and what will I lose if I stay at 2.4 (besides the modern gcc compiler and the other related dev tools)?"
if you're migrating, no doubt you're performing tests to ensure your product is still fit.
once you have your test plan ready, determining fitness against either kernel should be straight-forward.
2.4 is horrible to work with. It's missing so many features you expect from a POSIXy system that you constantly have to find work-arounds. Having a 2.4 kernel on the cluster during my PhD was enormous pain - I'd write code on FreeBSD, copy it to the cluster, and find half the features were missing. 2.6 is a lot better from a feature-standpoint, but is much heavier and isn't really suited to embedded systems anymore. If you're building the image yourself, why not go with FreeBSD or OpenBSD and get the best of both worlds - FreeBSD if you lean more towards features, OpenBSD if you want a smaller footprint?
I am TheRaven on Soylent News
I had the same question asked for an embedded project 3 years ago. And it was very clear cut then
2.6 you get (off the top of my head)
-Modern drivers (including USB/Network/etc)
-Various tick rates and tickless
-More support
-Several other improvements
So really don't bother w/ 2.4
how long until
http://www.linuxdevices.com/articles/AT7751365763.html
Without knowing your exact parameters though, it's hard to debate any specific advantages.
I suggest both a GCC 4 compiler (probably gcc-4.2 or 4.3) and a Linux 2.6 kernel (perhaps at least 2.6.25) with a fairly recent (ie 2.6 or 2.7) GNU libc Indeed, all this perhaps uses a bit more RAM, but you'll have more RAM than before, and it bring a lot of important functionalities & improvements (including bug fixes). If you need a specialized HTTP server, consider GNU libmicrohttpd Regard & Happy New Year 2009
If you foresee needing to periodically update the firmware to along with a library or app, then I would say a definitive YES - use the 2.6 kernel (assuming your device is supported).
It might also be the case that the board you would like to use is not supported in the 2.4 kernel if it's new enough - kernel developers usually don't want to waste time backporting their code if they can avoid it.
Which introduces the most important issue - backporting is a PITA!! To make a long story short, if you need to track a library or app, such as an embedded JRE, or a hardware interface that requires a kernel module inserted, playing catchup and needing to backport at the same time is an awful game of one-step-forward two-steps-back. Avoid it at all costs. Backporting is not always guaranteed to work!
The 2.4 kernel has a slightly faster boot time, while the 2.6 kernel has so many improvements that it's hard to shy away from. Do yourself a favour and go with a stable 2.6 kernel.
Lots of the improvements to 2.6 have probably been added to 2.4, but many come "native" to 2.6 so no outside patches are required. For example, kernel pre-emption, better scheduler, etc.. There are other intangibles too such as development time, testing, new toolchain, etc.., but you're already moving to a new processor and you'd have to do that anyway.
Sometime last year I was rebuilding some antique MIPS-based Linux from a 2.4 to a 2.6. Almost everything in the userspace was effortless (though much of it was based on Busybox); the main issue was related to some in-line assembler that took a while to figure out what it was doing. Once I did, I googled it and realized someone else had already solved a year or so ago.
So in short, no real benefit to sticking with 2.4 IMHO.
GCC 3.4 is quite outdated. 2.95 is just plain old. Why not code in Fortran while you're at it?
My development group is also stuck with gcc 2.9x series because it's only compiler our toolchain maker (WindRiver) supports for VxWorks 5.X. I'm guessing he's in a similar situation. I can't complain though -- we've never had an issue with it.
No clue what gp meant.
From all I heard (I was in embedded business only in 2.2/2.4 times) that 2.6 integrated some number of patches from embedded folks and generally can be customized to run on smaller number of resources. Also, the improved I/O (much lower latencies) and scheduler (interactivity; soft-real-time) would benefit in embedded too. 2.4 has number of problem related to memory management, when virtual memory subsystem can easily grab half of available RAM - only for supporting virtual memory. 2.6 solved the problem for most architectures.
Generally, many embedded folks moved to 2.6 already - mainly due to support for more new OTS hardware. 2.4 has this support only through vendor patches (e.g. I used in past BlueCat and MontaVista patches).
In my experience changing kernel on embedded system is quite easy task. Using development system within couple of days you can come up with suitable minimal .config (one needs development system since on target embedded systems might not have sufficient resources to run vanilla kernel). Generally it would either work or not. Normally it works.
Also note that H/W vendors started being more active in 2.6 times. In 2.4 times best shot at Linux driver was some crude port from e.g. LynxOS or VxWorks. From all I know, 2.6 now supports more PowerPC system than did patch from MontaVista for 2.4 I used three years ago.
Last, but not least, if you are looking at new modules, many hardware vendors supply Linux compatibility information. 2 years ago finding module with "Linux compatibility" chapter in documentation wasn't a problem at all.
All hope abandon ye who enter here.
Hi
We moved our project from 2.4 to 2.6 during development, because the maximum interrupt latency of 2.6 is so much better. We needed to handle UDP packets within 20 ms. max and occasionally on 2.4 we would have a 60 or more. Going to 2.6 solved our problems immediately, even with early versions.
See this Linux Journal article for more details on our project http://m.linuxjournal.com/article/7190
Bart van Deenen
Yes, 2.4.37 runs fine on an Asus EEE-Box (Atom, PCI-E, SATA, USB2, ...)
Willy
Your question feels a bit of strange question to ask as surely anyone who has looked would notice a huge difference between the latest 2.6 (2.6.28) and the latest 2.4 (2.4.37).
Preemptible kernel (so lower latencies are possible)
Far more devices supported (both in terms of architectures and additional add on devices e.g. SATA support)
Better scheduler (initially made O(1) scales better under load and then fairer with CFS)
Task Control Groups
Better support for threads (schedules them in a more intelligent fashion)
Strict overcommit
Massive VM changes
Tickless/dynticks support
Asynchronous I/O support
Introduction of different I/O schedulers (deadline, cfq
Network stack improvements (faster, better under load e.g. NAPI support)
epoll support
Improved ACPI support
Network filesystem improvements
Initramfs support
There is a huge list of Linux kernel changes that happened between 2.4 and 2.5. There is also a good Linux kernel 2.5 changes page on IBM's developerworks. Kernelnewbies has an excellent summary of changes for each of the 2.6 kernels and a 2.5 changes page. LWN is also excellent for kernel news.
I hate it when people don't bother to state exactly the points they object to. What other changes (not listed above) do you think the question poster wouldn't benefit from? Follow the links to the full lists (don't just use the ones off the top of your head)...