[PATCH 1/1] rcu: Remove redundant checks for rcu_scheduler_fully_active

[PATCH 1/1] rcu: Remove redundant checks for rcu_scheduler_fully_active

[Pranith Kumar]

rcu_scheduler_fully_active is set to true early in the boot process.

rcu_prepare_kthreads() is called in two locations. Once after setting the above
flag and the other while hotplugging a CPU from rcu_cpu_notify(). CPU hotplug is
enabled much later by which time the above flag is already set. Hence checking
for this flag is redundant in this function.

The checks in rcu_spawn_one_boost_kthread() and rcu_spawn_all_nocb_kthreads()
are similarly redundant.

This commit removes the redundant checks for this flag from the above
locations.

Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
---
 kernel/rcu/tree_plugin.h | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 17ccb62..a2113f6 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -1341,7 +1341,7 @@ static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
 	if (&rcu_preempt_state != rsp)
 		return 0;
 
-	if (!rcu_scheduler_fully_active || rnp->qsmaskinit == 0)
+	if (rnp->qsmaskinit == 0)
 		return 0;
 
 	rsp->boost = 1;
@@ -1489,8 +1489,7 @@ static void rcu_prepare_kthreads(int cpu)
 	struct rcu_node *rnp = rdp->mynode;
 
 	/* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
-	if (rcu_scheduler_fully_active)
-		(void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
+	(void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
 }
 
 #else /* #ifdef CONFIG_RCU_BOOST */
@@ -2509,9 +2508,8 @@ static void rcu_spawn_all_nocb_kthreads(int cpu)
 {
 	struct rcu_state *rsp;
 
-	if (rcu_scheduler_fully_active)
-		for_each_rcu_flavor(rsp)
-			rcu_spawn_one_nocb_kthread(rsp, cpu);
+	for_each_rcu_flavor(rsp)
+		rcu_spawn_one_nocb_kthread(rsp, cpu);
 }
 
 /*
-- 
1.9.1

Re: [PATCH 1/1] rcu: Remove redundant checks for rcu_scheduler_fully_active

[Paul E. McKenney]

On Tue, Jul 15, 2014 at 09:50:02PM -0400, Pranith Kumar wrote:
> rcu_scheduler_fully_active is set to true early in the boot process.
> 
> rcu_prepare_kthreads() is called in two locations. Once after setting the above
> flag and the other while hotplugging a CPU from rcu_cpu_notify(). CPU hotplug is
> enabled much later by which time the above flag is already set. Hence checking
> for this flag is redundant in this function.
> 
> The checks in rcu_spawn_one_boost_kthread() and rcu_spawn_all_nocb_kthreads()
> are similarly redundant.
> 
> This commit removes the redundant checks for this flag from the above
> locations.
> 
> Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>

Good catch!  Queued for 3.18.

							Thanx, Paul

> ---
>  kernel/rcu/tree_plugin.h | 10 ++++------
>  1 file changed, 4 insertions(+), 6 deletions(-)
> 
> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
> index 17ccb62..a2113f6 100644
> --- a/kernel/rcu/tree_plugin.h
> +++ b/kernel/rcu/tree_plugin.h
> @@ -1341,7 +1341,7 @@ static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
>  	if (&rcu_preempt_state != rsp)
>  		return 0;
> 
> -	if (!rcu_scheduler_fully_active || rnp->qsmaskinit == 0)
> +	if (rnp->qsmaskinit == 0)
>  		return 0;
> 
>  	rsp->boost = 1;
> @@ -1489,8 +1489,7 @@ static void rcu_prepare_kthreads(int cpu)
>  	struct rcu_node *rnp = rdp->mynode;
> 
>  	/* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
> -	if (rcu_scheduler_fully_active)
> -		(void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
> +	(void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
>  }
> 
>  #else /* #ifdef CONFIG_RCU_BOOST */
> @@ -2509,9 +2508,8 @@ static void rcu_spawn_all_nocb_kthreads(int cpu)
>  {
>  	struct rcu_state *rsp;
> 
> -	if (rcu_scheduler_fully_active)
> -		for_each_rcu_flavor(rsp)
> -			rcu_spawn_one_nocb_kthread(rsp, cpu);
> +	for_each_rcu_flavor(rsp)
> +		rcu_spawn_one_nocb_kthread(rsp, cpu);
>  }
> 
>  /*
> -- 
> 1.9.1
>