From a3667e3cef2ed00ba8f30b53c0ad1bfa66c8faa3 Mon Sep 17 00:00:00 2001 From: Steven Rostedt Date: Mon, 4 Nov 2013 20:27:36 -0500 Subject: [PATCH] rcu: Do not trace rcu_is_watching() functions As perf uses the rcu_read_lock() primitives for recording into its ring buffer, perf tracing can not be called when RCU in inactive. With the perf function tracing, there are functions that can be traced when RCU is not active, and perf must not have its function callback called when this is the case. Luckily, Paul McKenney has created a way to detect when RCU is active or not with the rcu_is_watching() function. Unfortunately, this function can also be traced, and if that happens it can cause a bit of overhead for the perf function calls that do the check. Recursion protection prevents anything bad from happening, but there is a bit of added overhead for every function being traced that must detect that the rcu_is_watching() is also being traced. As rcu_is_watching() is a helper routine and not part of the critical logic in RCU, it does not need to be traced in order to debug RCU itself. Add the "notrace" annotation to all the rcu_is_watching() calls such that we never trace it. Link: http://lkml.kernel.org/r/20131104202736.72dd8e45@gandalf.local.home Acked-by: Paul E. McKenney Signed-off-by: Steven Rostedt --- kernel/rcutiny.c | 2 +- kernel/rcutree.c | 4 ++-- 2 files changed, 3 insertions(+), 3 deletions(-) diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c index 0fa061dfa55db..590c8a82aa008 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 981d0c15a389e..499bb2b2198ca 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; -- 2.39.5