From mboxrd@z Thu Jan  1 00:00:00 1970
From: Sedat Dilek <sedat.dilek@gmail.com>
Subject: Re: linux-next: Tree for Feb 4
Date: Thu, 5 Feb 2015 22:45:59 +0100
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To: Steven Rostedt <rostedt@goodmis.org>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>, Dave Hansen <dave@sr71.net>, "Rafael J. Wysocki" <rjw@rjwysocki.net>, "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>, linux-next <linux-next@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>, Stephen Rothwell <sfr@canb.auug.org.au>, Kristen Carlson Accardi <kristen@linux.intel.com>, "H. Peter Anvin" <hpa@linux.intel.com>, Rik van Riel <riel@redhat.com>, Mel Gorman <mgorman@suse.de>

[...]
>>> >> 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 -