[PATCH tip/core/rcu 02/10] rcu: Use DEFINE_PER_CPU_SHARED_ALIGNED for rcu_data

From: Paul E. McKenney
Date: Tue Oct 28 2014 - 17:57:55 EST


From: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>

The rcu_data per-CPU variable has a number of fields that are atomically
manipulated, potentially by any CPU. This situation can result in false
sharing with per-CPU variables that have the misfortune of being allocated
adjacent to rcu_data in memory. This commit therefore changes the
DEFINE_PER_CPU() to DEFINE_PER_CPU_SHARED_ALIGNED() in order to avoid
this false sharing.

Reported-by: Christoph Lameter <cl@xxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Christoph Lameter <cl@xxxxxxxxx>
---
kernel/rcu/tree.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index c0673c56fb1a..ab6fcfb4fe11 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -105,7 +105,7 @@ struct rcu_state sname##_state = { \
.name = RCU_STATE_NAME(sname), \
.abbr = sabbr, \
}; \
-DEFINE_PER_CPU(struct rcu_data, sname##_data)
+DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_data, sname##_data)

RCU_STATE_INITIALIZER(rcu_sched, 's', call_rcu_sched);
RCU_STATE_INITIALIZER(rcu_bh, 'b', call_rcu_bh);
--
1.8.1.5

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