From 0209f6490b030f35349a2bb71294f3fd75b0f36d Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 14 Dec 2010 16:07:52 -0800 Subject: rcu: limit rcu_node leaf-level fanout Some recent benchmarks have indicated possible lock contention on the leaf-level rcu_node locks. This commit therefore limits the number of CPUs per leaf-level rcu_node structure to 16, in other words, there can be at most 16 rcu_data structures fanning into a given rcu_node structure. Prior to this, the limit was 32 on 32-bit systems and 64 on 64-bit systems. Note that the fanout of non-leaf rcu_node structures is unchanged. The organization of accesses to the rcu_node tree is such that references to non-leaf rcu_node structures are much less frequent than to the leaf structures. Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'kernel/rcutree.c') diff --git a/kernel/rcutree.c b/kernel/rcutree.c index c39ec5b4ae82..01c8ad33c510 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1869,8 +1869,9 @@ static void __init rcu_init_levelspread(struct rcu_state *rsp) { int i; - for (i = NUM_RCU_LVLS - 1; i >= 0; i--) + for (i = NUM_RCU_LVLS - 1; i > 0; i--) rsp->levelspread[i] = CONFIG_RCU_FANOUT; + rsp->levelspread[0] = RCU_FANOUT_LEAF; } #else /* #ifdef CONFIG_RCU_FANOUT_EXACT */ static void __init rcu_init_levelspread(struct rcu_state *rsp) -- cgit v1.2.3-58-ga151