Re: [patch V6 04/37] x86: Make hardware latency tracing explicit

[Thomas Gleixner]

Peter Zijlstra <peterz@xxxxxxxxxxxxx> writes:
> On Sat, May 16, 2020 at 01:45:51AM +0200, Thomas Gleixner wrote:
>> --- a/arch/x86/kernel/nmi.c
>> +++ b/arch/x86/kernel/nmi.c
>> @@ -334,6 +334,7 @@ static noinstr void default_do_nmi(struc
>>  	__this_cpu_write(last_nmi_rip, regs->ip);
>>  
>>  	instrumentation_begin();
>> +	ftrace_nmi_handler_enter();
>>  
>>  	handled = nmi_handle(NMI_LOCAL, regs);
>>  	__this_cpu_add(nmi_stats.normal, handled);
>> @@ -420,6 +421,7 @@ static noinstr void default_do_nmi(struc
>>  		unknown_nmi_error(reason, regs);
>>  
>>  out:
>> +	ftrace_nmi_handler_exit();
>>  	instrumentation_end();
>>  }
>
> Yeah, so I'm confused about this and the previous patch too. Why not
> do just this? Remove that ftrace_nmi_handler.* crud from
> nmi_{enter,exit}() and stick it here? Why do we needs the
> nmi_{enter,exit}_notrace() thing?

Because you then have to fixup _all_ architectures which use
nmi_enter/exit().

Thanks,

        tglx