As there is concern that the larger pcpu_list_node structure and the
per-cpu overhead may be a waste of resource on small system. This patch
adds a config parameter CONFIG_PERCPU_LIST to disable the per-cpu list
if the kernel builder chooses to do so. With per-cpu list disabled,
all the different groups of per-cpu lists will be degenerated into
global lists for all the CPUs.
The current default is to enable per-cpu list. A kernel builder needs
to explicitly turn it off.
Signed-off-by: Waiman Long <Waiman.Long@xxxxxxx>
---
fs/inode.c | 2 +-
include/linux/percpu-list.h | 93 ++++++++++++++++++++++++++++++++++++++++++-
lib/Kconfig | 14 ++++++
lib/percpu-list.c | 24 +++++++++++-
4 files changed, 130 insertions(+), 3 deletions(-)
diff --git a/fs/inode.c b/fs/inode.c
index 58d1a13..23e544b 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -437,7 +437,7 @@ EXPORT_SYMBOL_GPL(inode_sb_list_add);
static inline void inode_sb_list_del(struct inode *inode)
{
if (!list_empty(&inode->i_sb_list.list))
- pcpu_list_del(&inode->i_sb_list);
+ pcpu_list_del(&inode->i_sb_list, inode->i_sb->s_inodes);
}
static unsigned long hash(struct super_block *sb, unsigned long hashval)
diff --git a/include/linux/percpu-list.h b/include/linux/percpu-list.h
index fc6207f..12d75ad 100644
--- a/include/linux/percpu-list.h
+++ b/include/linux/percpu-list.h
@@ -80,6 +80,7 @@ static inline void init_pcpu_list_state(struct pcpu_list_state *state)
*/
#define pcpu_list_next_entry(pos, member) list_next_entry(pos, member.list)
+#ifdef CONFIG_PERCPU_LIST
/*
* Per-cpu node data structure
*/
@@ -212,7 +213,97 @@ static inline bool pcpu_list_iterate_safe(struct pcpu_list_head *head,
extern void pcpu_list_add(struct pcpu_list_node *node,
struct pcpu_list_head *head);
-extern void pcpu_list_del(struct pcpu_list_node *node);
+extern void pcpu_list_del(struct pcpu_list_node *node,
+ struct pcpu_list_head *head);
+
+#else /* CONFIG_PERCPU_LIST */
+
+#include <linux/slab.h>
+
+/*
+ * The per-cpu lists will now be degenerated into a single global list
+ */
+struct pcpu_list_node {
+ struct list_head list;
+};
+
+static inline void init_pcpu_list_node(struct pcpu_list_node *node)
+{
+ INIT_LIST_HEAD(&node->list);
+}
+
+static inline void free_pcpu_list_head(struct pcpu_list_head **phead)
+{
+ kfree(*phead);
+ *phead = NULL;
+}
+
+static inline bool pcpu_list_empty(struct pcpu_list_head *head)
+{
+ return list_empty(&head->list);
+}
+
+static inline void
+pcpu_list_add(struct pcpu_list_node *node, struct pcpu_list_head *head)
+{
+ spin_lock(&head->lock);
+ list_add(&node->list, &head->list);
+ spin_unlock(&head->lock);
+}
+
+static inline void
+pcpu_list_del(struct pcpu_list_node *node, struct pcpu_list_head *head)
+{
+ spin_lock(&head->lock);
+ list_del_init(&node->list);
+ spin_unlock(&head->lock);
+}
+
+static inline bool pcpu_list_iterate(struct pcpu_list_head *head,
+ struct pcpu_list_state *state)
+{
+ /*
+ * Find next entry
+ */
+ if (state->curr) {
+ state->curr = list_next_entry(state->curr, list);
+ } else {
+ spin_lock(&head->lock);
+ state->lock = &head->lock;
+ state->curr = list_entry(head->list.next,
+ struct pcpu_list_node, list);
+ }
+ if (&state->curr->list == &head->list) {
+ spin_unlock(&head->lock);
+ return false; /* The list has been exhausted */
+ }
+ return true; /* Continue the iteration */
+}
+
+static inline bool pcpu_list_iterate_safe(struct pcpu_list_head *head,
+ struct pcpu_list_state *state)
+{
+ /*
+ * Find next entry
+ */
+ if (state->curr) {
+ state->curr = state->next;
+ state->next = list_next_entry(state->next, list);
+ } else {
+ spin_lock(&head->lock);
+ state->lock = &head->lock;
+ state->curr = list_entry(head->list.next,
+ struct pcpu_list_node, list);
+ state->next = list_next_entry(state->curr, list);
+ }
+ if (&state->curr->list == &head->list) {
+ spin_unlock(&head->lock);
+ return false; /* The list has been exhausted */
+ }
+ return true; /* Continue the iteration */
+}
+#endif /* CONFIG_PERCPU_LIST */
+
extern int init_pcpu_list_head(struct pcpu_list_head **ppcpu_head);
#endif /* __LINUX_PERCPU_LIST_H */
diff --git a/lib/Kconfig b/lib/Kconfig
index 133ebc0..cdadc7e 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -536,4 +536,18 @@ config ARCH_HAS_PMEM_API
config ARCH_HAS_MMIO_FLUSH
bool
+#
+# Per-cpu list
+#
+config PERCPU_LIST
+ bool "Enable the use of per-cpu lists"
+ default y
+ depends on SMP
+ help
+ Enables the use of per-cpu list to allow parallel insertion
+ and deletion of list entry at the expense of a bit more
+ overhead in list iteration as well as larger list node entry.
+ This can help improve performance on system with a lot of
+ cpu cores.
+
endmenu
diff --git a/lib/percpu-list.c b/lib/percpu-list.c
index 5003bbb..46a91aa 100644
--- a/lib/percpu-list.c
+++ b/lib/percpu-list.c
@@ -24,6 +24,7 @@
*/
static struct lock_class_key percpu_list_key;
+#ifdef CONFIG_PERCPU_LIST
/*
* Initialize the per-cpu list head
*/
@@ -76,7 +77,7 @@ void pcpu_list_add(struct pcpu_list_node *node, struct pcpu_list_head *head)
* (becomes NULL or to a different one), we assume that the deletion was done
* elsewhere.
*/
-void pcpu_list_del(struct pcpu_list_node *node)
+void pcpu_list_del(struct pcpu_list_node *node, struct pcpu_list_head *unused)
{
spinlock_t *lock = READ_ONCE(node->lockptr);
@@ -98,3 +99,24 @@ void pcpu_list_del(struct pcpu_list_node *node)
}
spin_unlock(lock);
}
+
+#else /* CONFIG_PERCPU_LIST */
+/*
+ * Initialize the per-cpu list head
+ */
+int init_pcpu_list_head(struct pcpu_list_head **phead)
+{
+ struct pcpu_list_head *head = kmalloc(sizeof(struct pcpu_list_head),
+ GFP_KERNEL);
+
+ if (!head)
+ return -ENOMEM;
+
+ INIT_LIST_HEAD(&head->list);
+ head->lock = __SPIN_LOCK_UNLOCKED(&head->lock);
+ lockdep_set_class(&head->lock, &percpu_list_key);
+
+ *phead = head;
+ return 0;
+}
+#endif /* CONFIG_PERCPU_LIST */
--
1.7.1
--
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