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

[Peter Zijlstra]

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?