linux-kernel - Re: [PATCH 4/8] sched,rcu,tracing: Mark preempt_count

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Date:   Wed, 12 Feb 2020 16:02:11 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        mingo@...nel.org, joel@...lfernandes.org,
        gregkh@...uxfoundation.org, gustavo@...eddedor.com,
        tglx@...utronix.de, paulmck@...nel.org, josh@...htriplett.org,
        mathieu.desnoyers@...icios.com, jiangshanlai@...il.com
Subject: Re: [PATCH 4/8] sched,rcu,tracing: Mark preempt_count_{add,sub}()
 notrace

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@...radead.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.