Re: [PATCH] rcu: Do not trace rcu_is_watching() functions
From: Paul E. McKenney
Date: Tue Nov 05 2013 - 06:21:45 EST
On Mon, Nov 04, 2013 at 08:27:36PM -0500, Steven Rostedt wrote:
>
> Paul,
>
> As I added the rcu_is_watching() to the ftrace code to prevent perf
> from tracing functions where RCU is not watching, I noticed that the
> rcu_is_watching() functions can themselves be traced. I would say this
> is a helper function and not something that we need to trace, as it can
> cause a slowdown in function tracing (any recursion is detected, so it
> only affects performance).
>
> I marked the functions with notrace. You can take this patch and push
> it for 3.13 or I can take it if you give me an "Acked-by". As it only
> affects performance and does not crash the code it's not a must have in
> my tree.
>
> If you take it, I can write up a better change log too.
>
> -- Steve
>
> Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
Given an improved commit log:
Acked-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
> diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c
> index 0fa061d..590c8a8 100644
> --- a/kernel/rcutiny.c
> +++ b/kernel/rcutiny.c
> @@ -179,7 +179,7 @@ EXPORT_SYMBOL_GPL(rcu_irq_enter);
> /*
> * Test whether RCU thinks that the current CPU is idle.
> */
> -bool __rcu_is_watching(void)
> +bool notrace __rcu_is_watching(void)
> {
> return rcu_dynticks_nesting;
> }
> diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> index 981d0c1..499bb2b 100644
> --- a/kernel/rcutree.c
> +++ b/kernel/rcutree.c
> @@ -662,7 +662,7 @@ void rcu_nmi_exit(void)
> * rcu_is_watching(), the caller of __rcu_is_watching() must have at
> * least disabled preemption.
> */
> -bool __rcu_is_watching(void)
> +bool notrace __rcu_is_watching(void)
> {
> return atomic_read(this_cpu_ptr(&rcu_dynticks.dynticks)) & 0x1;
> }
> @@ -673,7 +673,7 @@ bool __rcu_is_watching(void)
> * If the current CPU is in its idle loop and is neither in an interrupt
> * or NMI handler, return true.
> */
> -bool rcu_is_watching(void)
> +bool notrace rcu_is_watching(void)
> {
> int ret;
>
>
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