Re: [PATCH 4/8] sched,rcu,tracing: Mark preempt_count_{add,sub}() notrace

Peter Zijlstra
2020-02-12T15:02:39Z

On Wed, Feb 12, 2020 at 09:24:17AM -0500, Steven Rostedt wrote:
> On Wed, 12 Feb 2020 10:32:14 +0100
> Peter Zijlstra <peterz@infradead.org> wrote:
>
> > Because of the requirement that no tracing happens until after we've
> > incremented preempt_count, see nmi_enter() / trace_rcu_enter(), mark
> > these functions as notrace.
>
> I actually depend on these function being traced.

Why? They already have a tracepoint inside.

> We do have
> "preempt_enable_notrace()" and "preempt_disable_notrace()" for places
> that shouldn't be traced. Can't we use those? (or simply
> __preempt_count_add()) in the nmi_enter() code instead? (perhaps create
> a preempt_count_add_notrace()).

My initial patch has __preempt_count_add/sub() in, but then I figured
someone would go complain the tracepoint would go missing.