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

[Peter Zijlstra]

On Mon, May 18, 2020 at 10:05:56AM +0200, Thomas Gleixner wrote:
> 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().

We probably have to anyway. But I can do that later I suppose.