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From:   Thomas Gleixner <tglx@linutronix.de>
To:     Steven Rostedt <rostedt@goodmis.org>
Cc:     LKML <linux-kernel@vger.kernel.org>, x86@kernel.org,
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Subject: Re: [patch V5 04/38] x86: Make hardware latency tracing explicit
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References: <20200512210059.056244513@linutronix.de> <20200512213809.784331304@linutronix.de> <20200514214349.24642172@oasis.local.home>
Date:   Fri, 15 May 2020 17:08:56 +0200
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Steven Rostedt <rostedt@goodmis.org> writes:

> On Tue, 12 May 2020 23:01:03 +0200
> Thomas Gleixner <tglx@linutronix.de> wrote:
>
>> --- a/arch/x86/kernel/cpu/mce/core.c
>> +++ b/arch/x86/kernel/cpu/mce/core.c
>> @@ -1916,7 +1916,7 @@ static __always_inline void exc_machine_
>>  	    mce_check_crashing_cpu())
>>  		return;
>>  
>> -	nmi_enter();
>> +	nmi_enter_notrace();
>
> Now a machine check exception could happen and be a cause of latency
> (although there may be more issues if it does). The "nmi_enter trace"
> version does two things. One is for time measurements (if available),
> and the other is just letting the hardware latency know it happen (a
> simple increment).
>
> The only thing that is checked is "smp_processor_id()" (I just
> remembered it doesn't need per cpu, as it only runs on a single CPU at
> a time).
>
> Could the notrace version supply the increment, and leave the
> trace_clock() in the trace version?

Yes, I can split it up that way.