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[PATCH tip/core/rcu 04/12] rcu: Cleanup rcu_init_geometry() code and arithmetics

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From: Alexander Gordeev <agordeev@redhat.com>

This update simplifies rcu_init_geometry() code flow
and makes calculation of the total number of rcu_node
structures more easy to read.

The update relies on the fact num_rcu_lvl[] is never
accessed beyond rcu_num_lvls index by the rest of the
code. Therefore, there is no need initialize the whole
num_rcu_lvl[].

Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Alexander Gordeev <agordeev@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/tree.c | 24 ++++++++++--------------
 1 file changed, 10 insertions(+), 14 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index ad49dbed44fb..37ca8a867a1c 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -4082,7 +4082,6 @@ static void __init rcu_init_geometry(void)
 {
 	ulong d;
 	int i;
-	int j;
 	int rcu_capacity[MAX_RCU_LVLS + 1];
 
 	/*
@@ -4135,24 +4134,21 @@ static void __init rcu_init_geometry(void)
 	if (nr_cpu_ids > rcu_capacity[MAX_RCU_LVLS])
 		panic("rcu_init_geometry: rcu_capacity[] is too small");
 
+	/* Calculate the number of levels in the tree. */
+	for (i = 1; nr_cpu_ids > rcu_capacity[i]; i++) {
+	}
+	rcu_num_lvls = i;
+
 	/* Calculate the number of rcu_nodes at each level of the tree. */
-	for (i = 1; i <= MAX_RCU_LVLS; i++)
-		if (nr_cpu_ids <= rcu_capacity[i]) {
-			for (j = 0; j <= i; j++) {
-				int cap = rcu_capacity[i - j];
-				num_rcu_lvl[j] = DIV_ROUND_UP(nr_cpu_ids, cap);
-			}
-			rcu_num_lvls = i;
-			for (j = i + 1; j <= MAX_RCU_LVLS; j++)
-				num_rcu_lvl[j] = 0;
-			break;
-		}
+	for (i = 0; i < rcu_num_lvls; i++) {
+		int cap = rcu_capacity[rcu_num_lvls - i];
+		num_rcu_lvl[i] = DIV_ROUND_UP(nr_cpu_ids, cap);
+	}
 
 	/* Calculate the total number of rcu_node structures. */
 	rcu_num_nodes = 0;
-	for (i = 0; i <= MAX_RCU_LVLS; i++)
+	for (i = 0; i < rcu_num_lvls; i++)
 		rcu_num_nodes += num_rcu_lvl[i];
-	rcu_num_nodes -= nr_cpu_ids;
 }
 
 /*
-- 
1.8.1.5

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[PATCH tip/core/rcu 0/12] Tree geometry-initialization  simplifications for 4.3 "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-18 00:40 +0200
  [PATCH tip/core/rcu 03/12] rcu: Remove superfluous local variable in rcu_init_geometry() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-18 00:40 +0200
  [PATCH tip/core/rcu 08/12] rcu: Remove unnecessary fields from rcu_state structure "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-18 00:40 +0200
  [PATCH tip/core/rcu 12/12] rcu: Reset rcu_fanout_leaf if out of bounds "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-18 00:40 +0200
  [PATCH tip/core/rcu 11/12] rcu: Shut up bogus gcc array bounds warning "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-18 00:40 +0200
  [PATCH tip/core/rcu 10/12] rcu: Simplify arithmetic to calculate number of RCU nodes "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-18 00:40 +0200
  [PATCH tip/core/rcu 05/12] rcu: Simplify rcu_init_geometry() capacity arithmetics "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-18 00:40 +0200
  [PATCH tip/core/rcu 09/12] rcu: Limit count of static data to the number of RCU levels "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-18 00:40 +0200
  [PATCH tip/core/rcu 01/12] rcu: Provide more diagnostics for stalled GP kthread "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-18 00:40 +0200
    [PATCH tip/core/rcu 04/12] rcu: Cleanup rcu_init_geometry() code and arithmetics "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-18 00:40 +0200
    [PATCH tip/core/rcu 02/12] rcu: Panic if RCU tree can not accommodate all CPUs "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-18 00:40 +0200
    [PATCH tip/core/rcu 07/12] rcu: Limit rcu_capacity[] size to RCU_NUM_LVLS items "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-18 00:40 +0200
    [PATCH tip/core/rcu 06/12] rcu: Limit rcu_state::levelcnt[] to RCU_NUM_LVLS items "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-07-18 00:40 +0200

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