From: Dipankar Sarma <dipankar@in.ibm.com>
This reduces the RCU head size by using a singly linked to maintain them.
The ordering of the callbacks is still maintained as before by using a tail
pointer for the next list.
Signed-Off-By : Dipankar Sarma <dipankar@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---
25-akpm/include/linux/rcupdate.h | 24 ++++++++++++----------
25-akpm/kernel/rcupdate.c | 42 +++++++++++++++++++--------------------
2 files changed, 34 insertions(+), 32 deletions(-)
diff -puN include/linux/rcupdate.h~singly-linked-rcu include/linux/rcupdate.h
--- 25/include/linux/rcupdate.h~singly-linked-rcu 2004-06-16 20:08:36.000000000 -0700
+++ 25-akpm/include/linux/rcupdate.h 2004-06-16 20:50:47.205019872 -0700
@@ -36,7 +36,6 @@
#ifdef __KERNEL__
#include <linux/cache.h>
-#include <linux/list.h>
#include <linux/spinlock.h>
#include <linux/threads.h>
#include <linux/percpu.h>
@@ -45,21 +44,20 @@
/**
* struct rcu_head - callback structure for use with RCU
- * @list: list_head to queue the update requests
+ * @next: next update requests in a list
* @func: actual update function to call after the grace period.
* @arg: argument to be passed to the actual update function.
*/
struct rcu_head {
- struct list_head list;
+ struct rcu_head *next;
void (*func)(void *obj);
void *arg;
};
-#define RCU_HEAD_INIT(head) \
- { .list = LIST_HEAD_INIT(head.list), .func = NULL, .arg = NULL }
+#define RCU_HEAD_INIT(head) { .next = NULL, .func = NULL, .arg = NULL }
#define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT(head)
#define INIT_RCU_HEAD(ptr) do { \
- INIT_LIST_HEAD(&(ptr)->list); (ptr)->func = NULL; (ptr)->arg = NULL; \
+ (ptr)->next = NULL; (ptr)->func = NULL; (ptr)->arg = NULL; \
} while (0)
@@ -99,8 +97,9 @@ struct rcu_data {
/* 2) batch handling */
long batch; /* Batch # for current RCU batch */
- struct list_head nxtlist;
- struct list_head curlist;
+ struct rcu_head *nxtlist;
+ struct rcu_head **nxttail;
+ struct rcu_head *curlist;
};
DECLARE_PER_CPU(struct rcu_data, rcu_data);
@@ -113,22 +112,25 @@ extern struct rcu_ctrlblk rcu_ctrlblk;
#define RCU_batch(cpu) (per_cpu(rcu_data, (cpu)).batch)
#define RCU_nxtlist(cpu) (per_cpu(rcu_data, (cpu)).nxtlist)
#define RCU_curlist(cpu) (per_cpu(rcu_data, (cpu)).curlist)
+#define RCU_nxttail(cpu) (per_cpu(rcu_data, (cpu)).nxttail)
static inline int rcu_pending(int cpu)
{
/* This cpu has pending rcu entries and the grace period
* for them has completed.
*/
- if (!list_empty(&RCU_curlist(cpu)) &&
+ if (RCU_curlist(cpu) &&
!rcu_batch_before(rcu_ctrlblk.completed,RCU_batch(cpu)))
return 1;
+
/* This cpu has no pending entries, but there are new entries */
- if (list_empty(&RCU_curlist(cpu)) &&
- !list_empty(&RCU_nxtlist(cpu)))
+ if (!RCU_curlist(cpu) && RCU_nxtlist(cpu))
return 1;
+
/* The rcu core waits for a quiescent state from the cpu */
if (RCU_quiescbatch(cpu) != rcu_ctrlblk.cur || RCU_qs_pending(cpu))
return 1;
+
/* nothing to do */
return 0;
}
diff -puN kernel/rcupdate.c~singly-linked-rcu kernel/rcupdate.c
--- 25/kernel/rcupdate.c~singly-linked-rcu 2004-06-16 20:08:36.225787200 -0700
+++ 25-akpm/kernel/rcupdate.c 2004-06-16 20:50:47.208019416 -0700
@@ -82,9 +82,11 @@ void fastcall call_rcu(struct rcu_head *
head->func = func;
head->arg = arg;
+ head->next = NULL;
local_irq_save(flags);
cpu = smp_processor_id();
- list_add_tail(&head->list, &RCU_nxtlist(cpu));
+ *RCU_nxttail(cpu) = head;
+ RCU_nxttail(cpu) = &head->next;
local_irq_restore(flags);
}
@@ -92,16 +94,14 @@ void fastcall call_rcu(struct rcu_head *
* Invoke the completed RCU callbacks. They are expected to be in
* a per-cpu list.
*/
-static void rcu_do_batch(struct list_head *list)
+static void rcu_do_batch(struct rcu_head *list)
{
- struct list_head *entry;
- struct rcu_head *head;
+ struct rcu_head *next;
- while (!list_empty(list)) {
- entry = list->next;
- list_del(entry);
- head = list_entry(entry, struct rcu_head, list);
- head->func(head->arg);
+ while (list) {
+ next = list->next;
+ list->func(list->arg);
+ list = next;
}
}
@@ -262,20 +262,21 @@ void rcu_restart_cpu(int cpu)
static void rcu_process_callbacks(unsigned long unused)
{
int cpu = smp_processor_id();
- LIST_HEAD(list);
+ struct rcu_head *rcu_list = NULL;
- if (!list_empty(&RCU_curlist(cpu)) &&
- !rcu_batch_before(rcu_ctrlblk.completed,RCU_batch(cpu))) {
- __list_splice(&RCU_curlist(cpu), &list);
- INIT_LIST_HEAD(&RCU_curlist(cpu));
+ if (RCU_curlist(cpu) &&
+ !rcu_batch_before(rcu_ctrlblk.completed, RCU_batch(cpu))) {
+ rcu_list = RCU_curlist(cpu);
+ RCU_curlist(cpu) = NULL;
}
local_irq_disable();
- if (!list_empty(&RCU_nxtlist(cpu)) && list_empty(&RCU_curlist(cpu))) {
+ if (RCU_nxtlist(cpu) && !RCU_curlist(cpu)) {
int next_pending, seq;
- __list_splice(&RCU_nxtlist(cpu), &RCU_curlist(cpu));
- INIT_LIST_HEAD(&RCU_nxtlist(cpu));
+ RCU_curlist(cpu) = RCU_nxtlist(cpu);
+ RCU_nxtlist(cpu) = NULL;
+ RCU_nxttail(cpu) = &RCU_nxtlist(cpu);
local_irq_enable();
/*
@@ -298,8 +299,8 @@ static void rcu_process_callbacks(unsign
local_irq_enable();
}
rcu_check_quiescent_state();
- if (!list_empty(&list))
- rcu_do_batch(&list);
+ if (rcu_list)
+ rcu_do_batch(rcu_list);
}
void rcu_check_callbacks(int cpu, int user)
@@ -315,8 +316,7 @@ static void __devinit rcu_online_cpu(int
{
memset(&per_cpu(rcu_data, cpu), 0, sizeof(struct rcu_data));
tasklet_init(&RCU_tasklet(cpu), rcu_process_callbacks, 0UL);
- INIT_LIST_HEAD(&RCU_nxtlist(cpu));
- INIT_LIST_HEAD(&RCU_curlist(cpu));
+ RCU_nxttail(cpu) = &RCU_nxtlist(cpu);
RCU_quiescbatch(cpu) = rcu_ctrlblk.completed;
RCU_qs_pending(cpu) = 0;
}
_