RT PREEMPT patches?

With the non-MMU Linux distribution you can select "preemptive Kernel" in "make menuconfig".,

I suppose it's the same with the Full Linux distribution, but I did not try yet.

-Michael

"Preemptive kernel" option makes critical sections non preemptible, unlike "Real-Time Preemptible Kernel" option of RT patch that does it.

Besides, RT patch requires a hardware high resolution timer (ACPI or HPET), lack of high resolution timers restricts real time applications.

Hi.

Do you use µClinux for NIOS II without MMU or Linux for NIOS II with MMU?

I think the best start is to use Linux for NIOS II with MMU because RT PREEMPT has been done for x86 with MMU first and modifies several Linux files but few files in the arch directory...

For synchronizing the Linux source for NIOS II and the RT PREEMPT patch, you may use a git command for having a new branch of the Linux source for NIOS II that is the nearest as possible of a RT PREEMPT patch version (with a commit id).

git command example:

$ git checkout -b preempt d01303a1035a39e445007c7522d89ad985c4153c

List of commit ids for stable branch nios2mmu here http://sopc.et.ntust.edu.tw/?p=linux-2.6.git;a=shortlog

Pat.

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Hi.

Do you use µClinux for NIOS II without MMU or Linux for NIOS II with MMU?

I think the best start is to use Linux for NIOS II with MMU because RT PREEMPT has been done for x86 with MMU first and modifies several Linux files but few files in the arch directory...

For synchronizing the Linux source for NIOS II and the RT PREEMPT patch, you may use a git command for having a new branch of the Linux source for NIOS II that is the nearest as possible of a RT PREEMPT patch version (with a commit id).

git command example:

$ git checkout -b preempt d01303a1035a39e445007c7522d89ad985c4153c

List of commit ids for stable branch nios2mmu here http://sopc.et.ntust.edu.tw/?p=linux-2.6.git;a=shortlog

Pat.

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I used the MMU version, I think that's the only reasonable approach since that's basically regular Linux.

I think checking out a nios2mmu branch/revision matching the Linux version of the RT branch would be a good start, but I would like to keep all the latest nios2 related changes (I am currently on unstable-nios2mmu), and my git-fu is lacking here. How would I get Linux 2.6.31 (or whatever the exact version I need for RT) but get the nios2 specific changes in unstable-nios2mmu? I am also concerned that if I try that I will run into the same types of issues I have with trying to merge 2.6.31-rt directly into unstable-nios2mmu.

Hi,

OK for the MMU version.

In the stable version, the Linux version is 2.6.30 (in the Makefile).

In the unstable version, the Linux version is 2.6.32-rc6.

You may apply the nearest RT patch to the NIOS Linux version and modify by hand rejected files (in the best case, juste sliding lines...).

But you have to modify some arch/nios2 files from scratch for porting RT PREEMPT. Have you read my PM on this point?

Pat.

Hippo:

Will the standard (MMU-based) include selecting the PREEMPT patches out of the box some day ?

I feel that is highly appropriate (if it does work).

-Michael

Hi,

Normal CONFIG_PREEMPT is working fine (of course, I don't know its efficiency). This configuration avoids the critical sections by only disabling the interruptions.

For CONFIG_PREEMPT_RT, you need not only to apply the patches but to make Nios's machine dependent codes which are very similar for SMP systems.

Kazu

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Hi,make Nios's machine dependent codes which are very similar for SMP systems.Kazu

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I feel that doing SMP System code for NIOS is a real challenge, as NIOS does not fave atomic instructions. I did some research on how it could be possible to provide a kind of Mutex with custom instructions that could be used to protect instruction sequences to make them atomic. I suppose this is possible and extensible to multiple CPUs, but you do need additional "hardware" to do this and I did not exactly proof that it might work.

Do you think this is needed to apply the CONFIG_PREEMPT_RT patch ?

-Michael

Hi,

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I feel that doing SMP System code for NIOS is a real challenge, as NIOS does not fave atomic instructions. I did some research on how it could be possible to provide a kind of Mutex with custom instructions that could be used to protect instruction sequences to make them atomic. I suppose this is possible and extensible to multiple CPUs, but you do need additional "hardware" to do this and I did not exactly proof that it might work.

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Several CPUs make 'Mutex' by using atomic instructions. But both for SMP system and CONFIG_PREEMPT_RT, we only need the 'Mutex' mechanism, not atomic instructions. And I don't think that we can make 'Mutex' by using custom instructions because there is no information about interrupt acception timing, pipeline behaviors and custom instructions.

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Do you think this is needed to apply the CONFIG_PREEMPT_RT patch ?

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We must enable the interruption in the critical section, so we need some kind of 'Mutex'.

Kazu