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Subject[PATCH tip/core/rcu 10/12] rcu: Make RCU able to tolerate undefined CONFIG_RCU_FANOUT
Date
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>

This commit introduces an RCU_FANOUT C-preprocessor macro so that RCU will
build even when CONFIG_RCU_FANOUT is undefined. The RCU_FANOUT macro is
set to the value of CONFIG_RCU_FANOUT when defined, otherwise it is set
to 32 for 32-bit systems and 64 for 64-bit systems. This commit then
makes CONFIG_RCU_FANOUT depend on CONFIG_RCU_EXPERT, so that Kconfig
users won't be asked about CONFIG_RCU_FANOUT unless they want to be.

Reported-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
init/Kconfig | 2 +-
kernel/rcu/tree.c | 4 ++--
kernel/rcu/tree.h | 17 ++++++++++++++---
kernel/rcu/tree_plugin.h | 6 +++---
4 files changed, 20 insertions(+), 9 deletions(-)

diff --git a/init/Kconfig b/init/Kconfig
index 35559e07db18..efb098ac159d 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -581,7 +581,7 @@ config RCU_FANOUT
int "Tree-based hierarchical RCU fanout value"
range 2 64 if 64BIT
range 2 32 if !64BIT
- depends on TREE_RCU || PREEMPT_RCU
+ depends on (TREE_RCU || PREEMPT_RCU) && RCU_EXPERT
default 64 if 64BIT
default 32 if !64BIT
help
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index c8b3700918e6..6fb8e2f0ec19 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3952,7 +3952,7 @@ static void __init rcu_init_levelspread(int *levelspread, const int *levelcnt)
if (rcu_fanout_exact) {
levelspread[rcu_num_lvls - 1] = rcu_fanout_leaf;
for (i = rcu_num_lvls - 2; i >= 0; i--)
- levelspread[i] = CONFIG_RCU_FANOUT;
+ levelspread[i] = RCU_FANOUT;
} else {
int ccur;
int cprv;
@@ -4083,7 +4083,7 @@ static void __init rcu_init_geometry(void)
*/
rcu_capacity[0] = rcu_fanout_leaf;
for (i = 1; i < RCU_NUM_LVLS; i++)
- rcu_capacity[i] = rcu_capacity[i - 1] * CONFIG_RCU_FANOUT;
+ rcu_capacity[i] = rcu_capacity[i - 1] * RCU_FANOUT;

/*
* The tree must be able to accommodate the configured number of CPUs.
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index f12fe832dbd3..ecb259273139 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -35,10 +35,21 @@
* In practice, this did work well going from three levels to four.
* Of course, your mileage may vary.
*/
+
+#ifdef CONFIG_RCU_FANOUT
+#define RCU_FANOUT CONFIG_RCU_FANOUT
+#else /* #ifdef CONFIG_RCU_FANOUT */
+# ifdef CONFIG_64BIT
+# define RCU_FANOUT 64
+# else
+# define RCU_FANOUT 32
+# endif
+#endif /* #else #ifdef CONFIG_RCU_FANOUT */
+
#define RCU_FANOUT_1 (CONFIG_RCU_FANOUT_LEAF)
-#define RCU_FANOUT_2 (RCU_FANOUT_1 * CONFIG_RCU_FANOUT)
-#define RCU_FANOUT_3 (RCU_FANOUT_2 * CONFIG_RCU_FANOUT)
-#define RCU_FANOUT_4 (RCU_FANOUT_3 * CONFIG_RCU_FANOUT)
+#define RCU_FANOUT_2 (RCU_FANOUT_1 * RCU_FANOUT)
+#define RCU_FANOUT_3 (RCU_FANOUT_2 * RCU_FANOUT)
+#define RCU_FANOUT_4 (RCU_FANOUT_3 * RCU_FANOUT)

#if NR_CPUS <= RCU_FANOUT_1
# define RCU_NUM_LVLS 1
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 074689cedda9..2e52502bfc95 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -70,10 +70,10 @@ static void __init rcu_bootup_announce_oddness(void)
{
if (IS_ENABLED(CONFIG_RCU_TRACE))
pr_info("\tRCU debugfs-based tracing is enabled.\n");
- if ((IS_ENABLED(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 64) ||
- (!IS_ENABLED(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 32))
+ if ((IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 64) ||
+ (!IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 32))
pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d\n",
- CONFIG_RCU_FANOUT);
+ RCU_FANOUT);
if (rcu_fanout_exact)
pr_info("\tHierarchical RCU autobalancing is disabled.\n");
if (IS_ENABLED(CONFIG_RCU_FAST_NO_HZ))
--
1.8.1.5


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