[PATCH tip/core/rcu 0/2] Tiny RCU updates for v4.1

[PATCH tip/core/rcu 0/2] Tiny RCU updates for v4.1

[Paul E. McKenney]

Hello!

This series contains some additional tinification for Tiny RCU:

1.	Remove redundant check from rcu_qsctr_help(), courtesy of
	Alexander Gordeev.

2.	Remove fastpath processing from __rcu_process_callbacks(),
	also courtesy of Alexander Gordeev.

							Thanx, Paul

------------------------------------------------------------------------

 b/kernel/rcu/tiny.c |   14 +-------------
 1 file changed, 1 insertion(+), 13 deletions(-)

[PATCH tip/core/rcu 1/2] rcu: Remove unnecessary condition check in rcu_qsctr_help()

[Paul E. McKenney]

From: Alexander Gordeev <agordeev@redhat.com>

When the ->curtail and ->donetail pointers differ, ->rcucblist
always points to the beginning of the current list and thus
cannot be NULL. Therefore, the check ->rcucblist != NULL is
redundant and this commit removes it.

Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/tiny.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c
index cc9ceca7bde1..d4e7fe5f3baf 100644
--- a/kernel/rcu/tiny.c
+++ b/kernel/rcu/tiny.c
@@ -103,8 +103,7 @@ EXPORT_SYMBOL(__rcu_is_watching);
 static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
 {
 	RCU_TRACE(reset_cpu_stall_ticks(rcp));
-	if (rcp->rcucblist != NULL &&
-	    rcp->donetail != rcp->curtail) {
+	if (rcp->donetail != rcp->curtail) {
 		rcp->donetail = rcp->curtail;
 		return 1;
 	}
-- 
1.8.1.5

[PATCH tip/core/rcu 2/2] rcu: Remove fastpath from __rcu_process_callbacks()

[Paul E. McKenney]

From: Alexander Gordeev <agordeev@redhat.com>

The standard code path accommodates a condition when no
RCU callbacks are ready to invoke. Since size of the code
is a priority for tiny RCU, remove the fast path.

Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/tiny.c | 11 -----------
 1 file changed, 11 deletions(-)

diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c
index d4e7fe5f3baf..069742d61c68 100644
--- a/kernel/rcu/tiny.c
+++ b/kernel/rcu/tiny.c
@@ -168,17 +168,6 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
 	unsigned long flags;
 	RCU_TRACE(int cb_count = 0);
 
-	/* If no RCU callbacks ready to invoke, just return. */
-	if (&rcp->rcucblist == rcp->donetail) {
-		RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, 0, -1));
-		RCU_TRACE(trace_rcu_batch_end(rcp->name, 0,
-					      !!ACCESS_ONCE(rcp->rcucblist),
-					      need_resched(),
-					      is_idle_task(current),
-					      false));
-		return;
-	}
-
 	/* Move the ready-to-invoke callbacks to a local list. */
 	local_irq_save(flags);
 	RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, rcp->qlen, -1));
-- 
1.8.1.5