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Tiny RCU updates for v4.1

PATCH New Paul E. McKenney 1 participant 3 messages Mar 3, 2015 RCU

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Paul E. McKenney

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#0 lore raw

cover Tiny RCU updates for v4.1

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(-)
author
#1 lore raw

PATCH 1/2 rcu: Remove unnecessary condition check in rcu_qsctr_help()

From: Alexander Gordeev <[email protected]>

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" <[email protected]>
Signed-off-by Alexander Gordeev <[email protected]>
Signed-off-by Paul E. McKenney <[email protected]>
---
 kernel/rcu/tiny.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)
kernel/rcu/tiny.c +1 -2
index cc9ceca7bde1..d4e7fe5f3baf 100644
@@ -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;
 	}
Signature · 1 line
1.8.1.5
author
#2 lore raw

PATCH 2/2 rcu: Remove fastpath from __rcu_process_callbacks()

From: Alexander Gordeev <[email protected]>

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" <[email protected]>
Signed-off-by Alexander Gordeev <[email protected]>
Signed-off-by Paul E. McKenney <[email protected]>
---
 kernel/rcu/tiny.c | 11 -----------
 1 file changed, 11 deletions(-)
kernel/rcu/tiny.c +0 -11
index d4e7fe5f3baf..069742d61c68 100644
@@ -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));
Signature · 1 line
1.8.1.5