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Commit 47d631af authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Make RCU able to tolerate undefined CONFIG_RCU_FANOUT_LEAF 



This commit introduces an RCU_FANOUT_LEAF C-preprocessor macro so
that RCU will build even when CONFIG_RCU_FANOUT_LEAF is undefined.
The RCU_FANOUT_LEAF macro is set to the value of CONFIG_RCU_FANOUT_LEAF
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_LEAF depend
on CONFIG_RCU_EXPERT, so that Kconfig users won't be asked about
CONFIG_RCU_FANOUT_LEAF unless they want to be.

Reported-by: default avatarIngo Molnar <mingo@kernel.org>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: default avatarPranith Kumar <bobby.prani@gmail.com>
parent 05c5df31

init/Kconfig

+1 −1
Original line number Diff line number Diff line
@@ -603,7 +603,7 @@ config RCU_FANOUT_LEAF 
	int "Tree-based hierarchical RCU leaf-level 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 16

	help

	  This option controls the leaf-level fanout of hierarchical

kernel/rcu/tree.c

+4 −4
Original line number Diff line number Diff line
@@ -119,8 +119,8 @@ module_param(dump_tree, bool, 0444); 
/* Control rcu_node-tree auto-balancing at boot time. */

static bool rcu_fanout_exact;

module_param(rcu_fanout_exact, bool, 0444);

/* Increase (but not decrease) the CONFIG_RCU_FANOUT_LEAF at boot time. */

static int rcu_fanout_leaf = CONFIG_RCU_FANOUT_LEAF;

/* Increase (but not decrease) the RCU_FANOUT_LEAF at boot time. */

static int rcu_fanout_leaf = RCU_FANOUT_LEAF;

module_param(rcu_fanout_leaf, int, 0444);

int rcu_num_lvls __read_mostly = RCU_NUM_LVLS;

static int num_rcu_lvl[] = {  /* Number of rcu_nodes at specified level. */
@@ -4097,7 +4097,7 @@ static void __init rcu_init_geometry(void) 
		jiffies_till_next_fqs = d;



	/* If the compile-time values are accurate, just leave. */

	if (rcu_fanout_leaf == CONFIG_RCU_FANOUT_LEAF &&

	if (rcu_fanout_leaf == RCU_FANOUT_LEAF &&

	    nr_cpu_ids == NR_CPUS)

		return;

	pr_info("RCU: Adjusting geometry for rcu_fanout_leaf=%d, nr_cpu_ids=%d\n",
@@ -4121,7 +4121,7 @@ static void __init rcu_init_geometry(void) 
	 * the configured number of CPUs.  Complain and fall back to the

	 * compile-time values if these limits are exceeded.

	 */

	if (rcu_fanout_leaf < CONFIG_RCU_FANOUT_LEAF ||

	if (rcu_fanout_leaf < RCU_FANOUT_LEAF ||

	    rcu_fanout_leaf > sizeof(unsigned long) * 8 ||

	    n > rcu_capacity[MAX_RCU_LVLS]) {

		WARN_ON(1);

kernel/rcu/tree.h

+11 −1
Original line number Diff line number Diff line
@@ -48,7 +48,17 @@ 
# endif

#endif /* #else #ifdef CONFIG_RCU_FANOUT */



#define RCU_FANOUT_1	      (CONFIG_RCU_FANOUT_LEAF)

#ifdef CONFIG_RCU_FANOUT_LEAF

#define RCU_FANOUT_LEAF CONFIG_RCU_FANOUT_LEAF

#else /* #ifdef CONFIG_RCU_FANOUT_LEAF */

# ifdef CONFIG_64BIT

# define RCU_FANOUT_LEAF 64

# else

# define RCU_FANOUT_LEAF 32

# endif

#endif /* #else #ifdef CONFIG_RCU_FANOUT_LEAF */



#define RCU_FANOUT_1	      (RCU_FANOUT_LEAF)

#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)

kernel/rcu/tree_plugin.h

+3 −3
Original line number Diff line number Diff line
@@ -76,10 +76,10 @@ static void __init rcu_bootup_announce_oddness(void) 
		pr_info("\tAdditional per-CPU info printed with stalls.\n");

	if (NUM_RCU_LVL_4 != 0)

		pr_info("\tFour-level hierarchy is enabled.\n");

	if (CONFIG_RCU_FANOUT_LEAF != 16)

	if (RCU_FANOUT_LEAF != 16)

		pr_info("\tBuild-time adjustment of leaf fanout to %d.\n",

			CONFIG_RCU_FANOUT_LEAF);

	if (rcu_fanout_leaf != CONFIG_RCU_FANOUT_LEAF)

			RCU_FANOUT_LEAF);

	if (rcu_fanout_leaf != RCU_FANOUT_LEAF)

		pr_info("\tBoot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf);

	if (nr_cpu_ids != NR_CPUS)

		pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids);