Re: [patch V5 04/38] x86: Make hardware latency tracing explicit

[Thomas Gleixner]

Steven Rostedt <rostedt@xxxxxxxxxxx> writes:

> On Tue, 12 May 2020 23:01:03 +0200
> Thomas Gleixner <tglx@xxxxxxxxxxxxx> 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.