[poky] RT-patch for Yocto-kernel

Bruce Ashfield bruce.ashfield at windriver.com
Wed Nov 6 21:16:05 PST 2013 

On 11/6/2013, 11:47 PM, Keskinarkaus, Teemu wrote:
> Okay, this gets interesting. Here is what I get:
>
> $ git branch | grep \*
> * standard/preempt-rt/base
> $ grep PREEMPT_RT_FULL kernel/Kconfig.preempt
> $
>
> And confirmed that also with menuconfig and the last two rt-options were missing from Preemption Model - selection.
>
> We are using emenlow KMACHINE if that has anything to do with it. Is it possible to use standard/preempt-rt/base and still not get those rt-patches for some reason? Sounds stupid, but something is keeping them from getting to the kernel.
>

Nope. These patches are not applied at build time, they are integrated
and applied to the tree at all times. Checking out the branch gets you
the changes. BUT, if you've set the SRCREV in your recipe to a value
that is before the patches are applied, then of course, the build system
will reset the tree and you won't see the changes.

If you can post all your recipes and layers, it would be easier to spot
what is wrong.

Bruce



> Teemu Keskinarkaus
>
> -----Original Message-----
> From: Bruce Ashfield [mailto:bruce.ashfield at windriver.com]
> Sent: 5. marraskuuta 2013 15:52
> To: Keskinarkaus, Teemu; Bruce Ashfield
> Cc: poky at yoctoproject.org
> Subject: Re: [poky] RT-patch for Yocto-kernel
>
> On 13-11-05 02:36 AM, Keskinarkaus, Teemu wrote:
>> Sorry for top post.
>>
>> I did some test. I compiled our project with linux-yocto-rt and linux-yocto - kernels.  Then checked from menuconfig that both of those kernels same options in:
>> Processor type and features ->  Preemption Model.
>> -> No Forced Preemption
>> -> Voluntary Kernel Preemption
>> -> Preemptible kernel
>>
>> When added rt-patch from: https://www.kernel.org/pub/linux/kernel/projects/rt/3.8/ I got two more options:
>>
>> -> Preemtible Kernel (Basic RT)
>> -> Fully Preememptible Kernel (RT)
>>
>> The fact that the rt-patch applied just fine to linux-yocto-rt - kernel sources got me thinking that the linux-yocto-rt does NOT contain the kernel.org rt-patch I mentioned earlier.  If that's the case then what's the point on whole rt-kernel branch? Or how do I get the rt-patched version of the kernel? When I compile the kernel I see that it uses linux-yocto-rt-3.8.13+gitAUTOINC+2a6d36e75c_47aed0c17c-r4.1 so it's not using the normal version of the kernel.
>
> I assure you .. it is applied. We've been applying and testing with the patch since Yocto 0.9, and longer pre-yocto.
>
> You aren't looking at the the right branches:
>
>   > git branch | grep \*
> * standard/preempt-rt/base
>
>   > grep PREEMPT_RT_FULL kernel/Kconfig.preempt
>           def_bool y if HAVE_PREEMPT_LAZY && PREEMPT_RT_FULL config PREEMPT_RT_FULL
>
>   > git whatchanged kernel/Kconfig.preempt
>
> commit abd0728b164f651292374e96251ee197b50e3c02
> Author: Bruce Ashfield <bruce.ashfield at windriver.com>
> Date:   Sun Mar 31 18:21:42 2013 -0700
>
>       preempt-rt: integrate patch-3.8.4-rt2
>
>       Merging patch-3.8.4-rt2 from:
> https://www.kernel.org/pub/linux/kernel/projects/rt/3.8/
>
>       From the release Notes:
>
>       changes since v3.8.4-rt1:
>          - build fix for i915 (reported by "Luis Claudio R. Goncalves")
>          - build fix for fscache (reported by tglx)
>          - build fix for !RT (kernel/softirq.c did not compile)
>          - per-cpu rwsem fixed for RT (required only by uprobes so far)
>          - slub: delay the execution of the ->ctor() hook for newly created
>            objects. This lowers the worst case latencies.
>
>       Known issues:
>
>             - SLxB is broken on PowerPC.
>
>       Signed-off-by: Bruce Ashfield <bruce.ashfield at windriver.com>
>
> :100644 100644 3f9c974... 38cecfe... M  kernel/Kconfig.preempt
>
> Cheers,
>
> Bruce
>
>>
>> Teemu Keskinarkaus
>>
>> -----Original Message-----
>> From: Bruce Ashfield [mailto:bruce.ashfield at gmail.com]
>> Sent: 4. marraskuuta 2013 15:17
>> To: Keskinarkaus, Teemu
>> Cc: poky at yoctoproject.org
>> Subject: Re: [poky] RT-patch for Yocto-kernel
>>
>> On Mon, Nov 4, 2013 at 2:31 AM, Keskinarkaus, Teemu <Teemu.Keskinarkaus at maximatecc.com> wrote:
>>> Hi,
>>>
>>>
>>>
>>> In our system we want to use Full RT - kernel configuration. I
>>> learned that Yocto/Poky Preempt - rt is actually just low latency
>>> configuration and not the real Full RT as the name falsely suggests.
>>> Anyway, that's not the problem after I found it.
>>>
>>
>> Hmm. No. The standard/preempt-rt/* branches in the Yocto kernel are the full -rt patch.
>>
>>>
>>>
>>> There is a patch in the kernel.org that adds the Full RT support for
>>> the kernel. Unfortunately it doesn't work right away in Yocto kernel.
>>> We use emenlow variant of the kernel.
>>>
>>>
>>>
>>> So I compiled the system and then fixed the patch by applying it to
>>> kernel sources in build-directory. Then added the  patch to kernel
>>> .bbappend file so that it would be applied during compilation time.  Or so I thought.
>>>
>>>
>>>
>>> Now when I try to compile the system do_patch - state for
>>> linux-yocto-rt - fails.
>>>
>>>
>>>
>>> Log data follows:
>>>
>>> | DEBUG: Executing shell function do_patch
>>>
>>> | Deleted branch meta-temp (was 37fdb0c).
>>>
>>> | [INFO] validating against known patches  (emenlow-preempt-rt-meta)
>>>
>>> Context reduced to (2/2) to apply fragment at 385    ] (\)(88 %))
>>>
>>> error: patch failed: drivers/net/ethernet/ti/cpsw.c:374(/)(92 %)%)
>>>
>>> | error: drivers/net/ethernet/ti/cpsw.c: patch does not apply
>>>
>>> | Context reduced to (1/1) to apply fragment at 1050
>>>
>>> | error: patch failed: include/linux/preempt.h:107
>>>
>>> | error: include/linux/preempt.h: patch does not apply
>>>
>>> | error: patch failed: kernel/sched/core.c:1477
>>>
>>> | error: kernel/sched/core.c: patch does not apply
>>>
>>> | ERROR. could not update git tree
>>>
>>> | ERROR. Could not apply patches for emenlow.
>>>
>>> |        Patch failures can be resolved in the devshell (bitbake -c
>>> | devshell
>>> linux-yocto-rt)
>>>
>>>
>>>
>>> If I'm understanding that right it actually applied my patch before
>>> the emenlow-patch and that's why it fails.
>>>
>>>
>>>
>>> What's the proper way to make kernel patch that big or is there
>>> already Full RT - patch for emenlow kernel for yocto? We have smaller
>>> patches that don't collide with emmenlow patches and they work just fine.
>>
>> You simply need to make the emenlow BSP compatible with linux-yocto-rt and use KBRANCH="standard/preempt-rt/base"
>>
>> And you have the full -rt patch available.
>>
>> Cheers,
>>
>> Bruce
>>
>>>
>>>
>>>
>>> Teemu Keskinarkaus
>>>
>>>
>>>
>>>
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>>
>>
>>
>> --
>> "Thou shalt not follow the NULL pointer, for chaos and madness await thee at its end"
>>
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>
>
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