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Subject[tip:core/rcu] rcu: Enable fourth level of TREE_RCU hierarchy
Commit-ID:  cf244dc01bf68e1ad338b82447f8686d24ea4435
Gitweb: http://git.kernel.org/tip/cf244dc01bf68e1ad338b82447f8686d24ea4435
Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
AuthorDate: Wed, 2 Dec 2009 12:10:14 -0800
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Thu, 3 Dec 2009 11:34:53 +0100

rcu: Enable fourth level of TREE_RCU hierarchy

Enable a fourth level of rcu_node hierarchy for TREE_RCU and
TREE_PREEMPT_RCU. This is for stress-testing and experiemental
purposes only, although in theory this would enable 16,777,216
CPUs on 64-bit systems, though only 1,048,576 CPUs on 32-bit
systems. Normal experimental use of this fourth level will
normally set CONFIG_RCU_FANOUT=2, requiring a 16-CPU system,
though the more adventurous (and more fortunate) experimenters
may wish to chose CONFIG_RCU_FANOUT=3 for 81-CPU systems or even
CONFIG_RCU_FANOUT=4 for 256-CPU systems.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Josh Triplett <josh@joshtriplett.org>
Acked-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference: <12597846161257-git-send-email->
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
kernel/rcutree.c | 6 +++++-
kernel/rcutree.h | 15 +++++++++++++--
2 files changed, 18 insertions(+), 3 deletions(-)
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index a9f5103..d47e03e 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -60,7 +60,8 @@ static struct lock_class_key rcu_node_class[NUM_RCU_LVLS];
NUM_RCU_LVL_0, /* root of hierarchy. */ \
NUM_RCU_LVL_1, \
NUM_RCU_LVL_2, \
- NUM_RCU_LVL_3, /* == MAX_RCU_LVLS */ \
+ NUM_RCU_LVL_3, \
+ NUM_RCU_LVL_4, /* == MAX_RCU_LVLS */ \
}, \
.signaled = RCU_GP_IDLE, \
.gpnum = -300, \
@@ -1877,6 +1878,9 @@ void __init rcu_init(void)
#ifdef CONFIG_RCU_CPU_STALL_DETECTOR
printk(KERN_INFO "RCU-based detection of stalled CPUs is enabled.\n");
#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
+#if NUM_RCU_LVL_4 != 0
+ printk(KERN_INFO "Experimental four-level hierarchy is enabled.\n");
+#endif /* #if NUM_RCU_LVL_4 != 0 */
RCU_INIT_FLAVOR(&rcu_sched_state, rcu_sched_data);
RCU_INIT_FLAVOR(&rcu_bh_state, rcu_bh_data);
__rcu_init_preempt();
diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index 8bb03cb..df2e0b6 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -34,10 +34,11 @@
* In practice, this has not been tested, so there is probably some
* bug somewhere.
*/
-#define MAX_RCU_LVLS 3
+#define MAX_RCU_LVLS 4
#define RCU_FANOUT (CONFIG_RCU_FANOUT)
#define RCU_FANOUT_SQ (RCU_FANOUT * RCU_FANOUT)
#define RCU_FANOUT_CUBE (RCU_FANOUT_SQ * RCU_FANOUT)
+#define RCU_FANOUT_FOURTH (RCU_FANOUT_CUBE * RCU_FANOUT)

#if NR_CPUS <= RCU_FANOUT
# define NUM_RCU_LVLS 1
@@ -45,23 +46,33 @@
# define NUM_RCU_LVL_1 (NR_CPUS)
# define NUM_RCU_LVL_2 0
# define NUM_RCU_LVL_3 0
+# define NUM_RCU_LVL_4 0
#elif NR_CPUS <= RCU_FANOUT_SQ
# define NUM_RCU_LVLS 2
# define NUM_RCU_LVL_0 1
# define NUM_RCU_LVL_1 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT)
# define NUM_RCU_LVL_2 (NR_CPUS)
# define NUM_RCU_LVL_3 0
+# define NUM_RCU_LVL_4 0
#elif NR_CPUS <= RCU_FANOUT_CUBE
# define NUM_RCU_LVLS 3
# define NUM_RCU_LVL_0 1
# define NUM_RCU_LVL_1 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_SQ)
# define NUM_RCU_LVL_2 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT)
# define NUM_RCU_LVL_3 NR_CPUS
+# define NUM_RCU_LVL_4 0
+#elif NR_CPUS <= RCU_FANOUT_FOURTH
+# define NUM_RCU_LVLS 4
+# define NUM_RCU_LVL_0 1
+# define NUM_RCU_LVL_1 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_CUBE)
+# define NUM_RCU_LVL_2 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT_SQ)
+# define NUM_RCU_LVL_3 DIV_ROUND_UP(NR_CPUS, RCU_FANOUT)
+# define NUM_RCU_LVL_4 NR_CPUS
#else
# error "CONFIG_RCU_FANOUT insufficient for NR_CPUS"
#endif /* #if (NR_CPUS) <= RCU_FANOUT */

-#define RCU_SUM (NUM_RCU_LVL_0 + NUM_RCU_LVL_1 + NUM_RCU_LVL_2 + NUM_RCU_LVL_3)
+#define RCU_SUM (NUM_RCU_LVL_0 + NUM_RCU_LVL_1 + NUM_RCU_LVL_2 + NUM_RCU_LVL_3 + NUM_RCU_LVL_4)
#define NUM_RCU_NODES (RCU_SUM - NR_CPUS)

/*

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