linux-kernel - [PATCH tip/core/rcu 2/2] rcu: Remove fastpath from __rcu_process

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Date:	Tue,  3 Mar 2015 09:53:36 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	mingo@...nel.org, laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
	rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
	dvhart@...ux.intel.com, fweisbec@...il.com, oleg@...hat.com,
	bobby.prani@...il.com, Alexander Gordeev <agordeev@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 2/2] rcu: Remove fastpath from __rcu_process_callbacks()

From: Alexander Gordeev <agordeev@...hat.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@...ux.vnet.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@...hat.com>
Signed-off-by: Paul E. McKenney <paulmck@...ux.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

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