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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2009-08-22 13:56:52 -0700
committerIngo Molnar <mingo@elte.hu>2009-08-23 10:32:40 +0200
commitf41d911f8c49a5d65c86504c19e8204bb605c4fd (patch)
tree59bcd3048652ef290b3e19d2904409afd5c90eb3 /kernel/rcutree.h
parenta157229cabd6dd8cfa82525fc9bf730c94cc9ac2 (diff)
rcu: Merge preemptable-RCU functionality into hierarchical RCU
Create a kernel/rcutree_plugin.h file that contains definitions for preemptable RCU (or, under the #else branch of the #ifdef, empty definitions for the classic non-preemptable semantics). These definitions fit into plugins defined in kernel/rcutree.c for this purpose. This variant of preemptable RCU uses a new algorithm whose read-side expense is roughly that of classic hierarchical RCU under CONFIG_PREEMPT. This new algorithm's update-side expense is similar to that of classic hierarchical RCU, and, in absence of read-side preemption or blocking, is exactly that of classic hierarchical RCU. Perhaps more important, this new algorithm has a much simpler implementation, saving well over 1,000 lines of code compared to mainline's implementation of preemptable RCU, which will hopefully be retired in favor of this new algorithm. The simplifications are obtained by maintaining per-task nesting state for running tasks, and using a simple lock-protected algorithm to handle accounting when tasks block within RCU read-side critical sections, making use of lessons learned while creating numerous user-level RCU implementations over the past 18 months. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: akpm@linux-foundation.org Cc: mathieu.desnoyers@polymtl.ca Cc: josht@linux.vnet.ibm.com Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org LKML-Reference: <12509746134003-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/rcutree.h')
-rw-r--r--kernel/rcutree.h9
1 files changed, 9 insertions, 0 deletions
diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index 0024e5ddcc68..ca560364d8cd 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -80,6 +80,7 @@ struct rcu_dynticks {
*/
struct rcu_node {
spinlock_t lock;
+ long gpnum; /* Current grace period for this node. */
unsigned long qsmask; /* CPUs or groups that need to switch in */
/* order for current grace period to proceed.*/
unsigned long qsmaskinit;
@@ -90,6 +91,8 @@ struct rcu_node {
u8 grpnum; /* CPU/group number for next level up. */
u8 level; /* root is at level 0. */
struct rcu_node *parent;
+ struct list_head blocked_tasks[2];
+ /* Tasks blocked in RCU read-side critsect. */
} ____cacheline_internodealigned_in_smp;
/* Index values for nxttail array in struct rcu_data. */
@@ -111,6 +114,7 @@ struct rcu_data {
bool passed_quiesc; /* User-mode/idle loop etc. */
bool qs_pending; /* Core waits for quiesc state. */
bool beenonline; /* CPU online at least once. */
+ bool preemptable; /* Preemptable RCU? */
struct rcu_node *mynode; /* This CPU's leaf of hierarchy */
unsigned long grpmask; /* Mask to apply to leaf qsmask. */
@@ -244,5 +248,10 @@ DECLARE_PER_CPU(struct rcu_data, rcu_sched_data);
extern struct rcu_state rcu_bh_state;
DECLARE_PER_CPU(struct rcu_data, rcu_bh_data);
+#ifdef CONFIG_TREE_PREEMPT_RCU
+extern struct rcu_state rcu_preempt_state;
+DECLARE_PER_CPU(struct rcu_data, rcu_preempt_data);
+#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
+
#endif /* #ifdef RCU_TREE_NONCORE */