[linux-yocto] [yocto-kernel-cache][PATCH] features/systemtap/systemtap.cfg: enable CONFIG_KERNEL_DEBUG

Victor Kamensky kamensky at cisco.com
Wed Mar 14 07:41:50 PDT 2018

Hi Bruce,

On Wed, 14 Mar 2018, Bruce Ashfield wrote:

> As it turns out, Ross is reporting a big performance degradation in the kernel
> in footprint, packaging and build time.
> It completely slipped my mind when looking at this commit, that we went through
> a split two years ago for that very same issue.
> For now, I'm going to revert this,

Please note that after revert in your regular build kernels will not
be debuggable, because it is missing symbols. For example for 
investigation like [1] where kernel hangs where one can pick at
hangged kernel quickly after 'runnqemu qemuparam="-S -s"'. It is
not possible without symbols.

> and then work systemtap properly into the
> developer kernel type. The issue is that the standard kernel includes systemtap
> by default (it probably shouldn't), and hence is picking up the DEBUG_KERNEL
> option .. and that's causing the issues.

Even if you revert commit please do not remove systemtap fragment
from regular kernel. I said that without CONFIG_KERNEL_DEBUG
kernel tracing does not make sense. But besides kernel systemtap
can do user-land process tracing, this one works OK even if symbols
are not in kernel.

Instead of removing systemtap.cfg from regular kernel, it would be
better to add separate debuginfo.cfg that would enable debug
symbols kernle and have some quick way through which one can add
symbols through simple local.conf setting. So if run into situation
like [1], and need to look at kernel with gdb or run systemtap
against it, one can just add line to local.conf and rebuild kernel.



> For now, you can build the developer kernel type, or add the developer kernel
> configuration fragment via a bbappend, and you'll have a functional systemtap.
> I can move systemtap out of the standard kernel and only into the developer
> kernel, since as you say, it isn't functional without this option.
> But, that ktype
> hasn't gotten a lot of mileage (despite being around for two years),
> so I'll need
> to run some tests before I can truly move the fragment over and confirm that
> it works.
> So again, for now, I'll revert this, but will work on getting the
> ktypes fixed up
> as well.
> Cheers,
> Bruce
> commit a7b57bb54cace686911faae9a8eace3b9cbf8145
> Author: California Sullivan <california.l.sullivan at intel.com>
> Date:   Wed Feb 17 16:47:10 2016 -0800
>    ktypes: add developer ktype
>    The developer ktype enables EMBEDDED, EXPERT, and DEBUG_KERNEL,
>    opening up more kernel options and setting some defaults.
>    Signed-off-by: California Sullivan <california.l.sullivan at intel.com>
>    Signed-off-by: Bruce Ashfield <bruce.ashfield at windriver.com>
> :000000 100644 000000000000... ee04ec720188... A
> ktypes/developer/developer.cfg
> :000000 100644 000000000000... cf2c0e6519d5... A
> ktypes/developer/developer.scc
> On Sat, Mar 3, 2018 at 9:03 PM, Victor Kamensky <kamensky at cisco.com> wrote:
>> Need to enable CONFIG_KERNEL_DEBUG in systemtap feature, otherwise
>> CONFIG_DEBUG_INFO set by systemtap.cfg does not have any effect since
>> it depends on CONFIG_KERNEL_DEBUG and is set off in resulting config.
>> So systemtap cannot find DWARF information in resulting kernel.
>> Signed-off-by: Victor Kamensky <kamensky at cisco.com>
>> ---
>>  features/systemtap/systemtap.cfg | 1 +
>>  1 file changed, 1 insertion(+)
>> diff --git a/features/systemtap/systemtap.cfg b/features/systemtap/systemtap.cfg
>> index acc2405..858447c 100644
>> --- a/features/systemtap/systemtap.cfg
>> +++ b/features/systemtap/systemtap.cfg
>> @@ -1,4 +1,5 @@
>> --
>> 2.7.4
>> --
>> _______________________________________________
>> linux-yocto mailing list
>> linux-yocto at yoctoproject.org
>> https://lists.yoctoproject.org/listinfo/linux-yocto
> -- 
> "Thou shalt not follow the NULL pointer, for chaos and madness await
> thee at its end"

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