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

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Message-ID: <20200212092417.04c3da8c@gandalf.local.home>
Date:   Wed, 12 Feb 2020 09:24:17 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Peter Zijlstra <peterz@...radead.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, 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. 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()).

-- Steve



> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>  kernel/sched/core.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -3781,7 +3781,7 @@ static inline void preempt_latency_start
>  	}
>  }
>  
> -void preempt_count_add(int val)
> +void notrace preempt_count_add(int val)
>  {
>  #ifdef CONFIG_DEBUG_PREEMPT
>  	/*
> @@ -3813,7 +3813,7 @@ static inline void preempt_latency_stop(
>  		trace_preempt_on(CALLER_ADDR0, get_lock_parent_ip());
>  }
>  
> -void preempt_count_sub(int val)
> +void notrace preempt_count_sub(int val)
>  {
>  #ifdef CONFIG_DEBUG_PREEMPT
>  	/*
>