Re: linux-next: Tree for Feb 4

Sedat Dilek
2015-02-05T21:46:04Z

[...]
>>> >> Unfortunately, the call-trace remains when doing an offlining of cpu1.
>>> >> ( It's good to see it's reproducible. )
>>> >
>>> > Was the tracepoint enabled? Or was there some other rcu call that
>>> > triggered this. Or would cpu_online(smp_processor_id()) return true at
>>> > this point?
>>> >
>>>
>>> Thanks Steve for jumping into this one!
>>>
>>> Good point.
>>> I looked at my kernel-config (which I already sent :-)).
>>>
>>> Do I need to enable...?
>>>
>>> # CONFIG_RCU_TRACE is not set
>>>
>>> ...or even more?
>>>
>>
>> What I meant by the tracepoint being enabled, was not that it was
>> configured in (I'm assuming it was), but that you started tracing?
>>
>> echo 1 > /sys/kernel/debug/tracing/events/enable
>>
>> or
>>
>> echo 1 > /sys/kernel/debug/tracing/events/tlb/tlb_flushed/enable
>>
>
> NO, I did not start any tracing before doing my testing.
>
> # cat /sys/kernel/debug/tracing/events/enable
> 0
>
> # echo 1 > /sys/kernel/debug/tracing/events/enable
>
> # cat /sys/kernel/debug/tracing/events/enable
> X
>
> # LC_ALL=C cat /sys/kernel/debug/tracing/events/tlb/tlb_flushed/enable
> cat: /sys/kernel/debug/tracing/events/tlb/tlb_flushed/enable: No such
> file or directory
>
> Looks like I need to enable...?
>
> # CONFIG_DEBUG_TLBFLUSH is not set
>

Here my new kernel-config (not sure if I really need them to be enabled):

$ ./scripts/diffconfig
/boot/config-3.19.0-rc7-next-20150204.7-iniza-small
/boot/config-3.19.0-rc7-next-20150204.9-iniza-small
DEBUG_TLBFLUSH n -> y
RCU_TRACE n -> y
TREE_RCU_TRACE n -> y

Steve, this was a typo it's called tlb_flush not tlb_flush*ed*:

# cat /sys/kernel/debug/tracing/events/tlb/tlb_flush/enable
1

[ 391.090381] intel_pstate CPU 1 exiting
[ 391.104491] smpboot: CPU 1 is now offline

- Sedat -