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Commit 05c5df31 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Make RCU able to tolerate undefined CONFIG_RCU_FANOUT 



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: 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 8739c5cb

init/Kconfig

+1 −1
Original line number Diff line number Diff line
@@ -583,7 +583,7 @@ 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

kernel/rcu/tree.c

+2 −2
Original line number Diff line number Diff line
@@ -3971,7 +3971,7 @@ static void __init rcu_init_levelspread(struct rcu_state *rsp) 
	if (rcu_fanout_exact) {

		rsp->levelspread[rcu_num_lvls - 1] = rcu_fanout_leaf;

		for (i = rcu_num_lvls - 2; i >= 0; i--)

			rsp->levelspread[i] = CONFIG_RCU_FANOUT;

			rsp->levelspread[i] = RCU_FANOUT;

	} else {

		int ccur;

		int cprv;
@@ -4111,7 +4111,7 @@ static void __init rcu_init_geometry(void) 
	rcu_capacity[0] = 1;

	rcu_capacity[1] = rcu_fanout_leaf;

	for (i = 2; i <= MAX_RCU_LVLS; i++)

		rcu_capacity[i] = rcu_capacity[i - 1] * CONFIG_RCU_FANOUT;

		rcu_capacity[i] = rcu_capacity[i - 1] * RCU_FANOUT;



	/*

	 * The boot-time rcu_fanout_leaf parameter is only permitted

kernel/rcu/tree.h

+15 −3
Original line number Diff line number Diff line
@@ -35,11 +35,23 @@ 
 * In practice, this did work well going from three levels to four.

 * Of course, your mileage may vary.

 */



#define MAX_RCU_LVLS 4



#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

kernel/rcu/tree_plugin.h

+3 −3
Original line number Diff line number Diff line
@@ -60,10 +60,10 @@ 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))