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

[Bruce Ashfield]

On 2018-03-14 10:41 AM, Victor Kamensky wrote:
> 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.

That's fully understood. But we cannot have that config on for
the standard kernel build. That's what the developer ktype is for.

> 
>> 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.

There's already a fragment for that purpose and it is what the
developer kernel type uses. Anyone can include that fragment via
a bbappend.

The developer kernel type includes the standard kernel, so it is
a superset .. so yes, I can leave systemtap in place and the developer
kernel type just finishes the enablement of it.

Bruce

> 
> [1] 
> http://lists.openembedded.org/pipermail/openembedded-core/2018-March/148587.html 
> 
> 
> Thanks,
> Victor
> 
>> 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 @@
>>>  CONFIG_RELAY=y
>>> +CONFIG_DEBUG_KERNEL=y
>>>  CONFIG_DEBUG_INFO=y
>>>  CONFIG_DEBUG_FS=y
>>>  CONFIG_MODULES=y
>>> -- 
>>> 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"
>>