lkml.org 
[lkml]   [2016]   [Apr]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH v7 1/4] lib/percpu-list: Per-cpu list with associated per-cpu locks
Date
Linked list is used everywhere in the Linux kernel. However, if many
threads are trying to add or delete entries into the same linked list,
it can create a performance bottleneck.

This patch introduces a new per-cpu list subystem with associated
per-cpu locks for protecting each of the lists individually. This
allows list entries insertion and deletion operations to happen in
parallel instead of being serialized with a global list and lock.

List entry insertion is strictly per cpu. List deletion, however, can
happen in a cpu other than the one that did the insertion. So we still
need lock to protect the list. Because of that, there may still be
a small amount of contention when deletion is being done.

A new header file include/linux/percpu-list.h will be added with the
associated pcpu_list_head and pcpu_list_node structures. The following
functions are provided to manage the per-cpu list:

1. int init_pcpu_list_head(struct pcpu_list_head **ppcpu_head)
2. void pcpu_list_add(struct pcpu_list_node *node,
struct pcpu_list_head *head)
3. void pcpu_list_del(struct pcpu_list *node)

Iteration of all the list entries within a group of per-cpu
lists is done by calling either the pcpu_list_iterate() or
pcpu_list_iterate_safe() functions in a while loop. They correspond
to the list_for_each_entry() and list_for_each_entry_safe() macros
respectively. The iteration states are keep in a pcpu_list_state
structure that is passed to the iteration functions.

Signed-off-by: Waiman Long <Waiman.Long@hpe.com>
---
include/linux/percpu-list.h | 231 +++++++++++++++++++++++++++++++++++++++++++
lib/Makefile | 2 +-
lib/percpu-list.c | 100 +++++++++++++++++++
3 files changed, 332 insertions(+), 1 deletions(-)
create mode 100644 include/linux/percpu-list.h
create mode 100644 lib/percpu-list.c

diff --git a/include/linux/percpu-list.h b/include/linux/percpu-list.h
new file mode 100644
index 0000000..ce8238a
--- /dev/null
+++ b/include/linux/percpu-list.h
@@ -0,0 +1,231 @@
+/*
+ * Per-cpu list
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * (C) Copyright 2016 Hewlett-Packard Enterprise Development LP
+ *
+ * Authors: Waiman Long <waiman.long@hpe.com>
+ */
+#ifndef __LINUX_PERCPU_LIST_H
+#define __LINUX_PERCPU_LIST_H
+
+#include <linux/spinlock.h>
+#include <linux/list.h>
+#include <linux/percpu.h>
+
+/*
+ * include/linux/percpu-list.h
+ *
+ * A per-cpu list protected by a per-cpu spinlock.
+ *
+ * The pcpu_list_head structure contains the spinlock, the other
+ * pcpu_list_node structures only contains a pointer to the spinlock in
+ * pcpu_list_head.
+ */
+struct pcpu_list_head {
+ struct list_head list;
+ spinlock_t lock;
+};
+
+#define PCPU_LIST_HEAD_INIT(name) \
+ { \
+ .list.prev = &name.list, \
+ .list.next = &name.list, \
+ .list.lock = __SPIN_LOCK_UNLOCKED(name), \
+ }
+
+/*
+ * Per-cpu list iteration state
+ */
+struct pcpu_list_state {
+ int cpu;
+ spinlock_t *lock;
+ struct list_head *head; /* List head of current per-cpu list */
+ struct pcpu_list_node *curr;
+ struct pcpu_list_node *next;
+};
+
+#define PCPU_LIST_STATE_INIT() \
+ { \
+ .cpu = -1, \
+ .lock = NULL, \
+ .head = NULL, \
+ .curr = NULL, \
+ .next = NULL, \
+ }
+
+#define DEFINE_PCPU_LIST_STATE(s) \
+ struct pcpu_list_state s = PCPU_LIST_STATE_INIT()
+
+static inline void init_pcpu_list_state(struct pcpu_list_state *state)
+{
+ state->cpu = -1;
+ state->lock = NULL;
+ state->head = NULL;
+ state->curr = NULL;
+ state->next = NULL;
+}
+
+#ifdef CONFIG_DEBUG_SPINLOCK
+#define PERCPU_LIST_WARN_ON(x) WARN_ON(x)
+#else
+#define PERCPU_LIST_WARN_ON(x)
+#endif
+
+/*
+ * Next per-cpu list entry
+ */
+#define pcpu_list_next_entry(pos, member) list_next_entry(pos, member.list)
+
+/*
+ * Per-cpu node data structure
+ */
+struct pcpu_list_node {
+ struct list_head list;
+ spinlock_t *lockptr;
+};
+
+#define PCPU_LIST_NODE_INIT(name) \
+ { \
+ .list.prev = &name.list, \
+ .list.next = &name.list, \
+ .list.lockptr = NULL \
+ }
+
+static inline void init_pcpu_list_node(struct pcpu_list_node *node)
+{
+ INIT_LIST_HEAD(&node->list);
+ node->lockptr = NULL;
+}
+
+static inline void free_pcpu_list_head(struct pcpu_list_head **ppcpu_head)
+{
+ free_percpu(*ppcpu_head);
+ *ppcpu_head = NULL;
+}
+
+/*
+ * Check if all the per-cpu lists are empty
+ */
+static inline bool pcpu_list_empty(struct pcpu_list_head *pcpu_head)
+{
+ int cpu;
+
+ for_each_possible_cpu(cpu)
+ if (!list_empty(&per_cpu_ptr(pcpu_head, cpu)->list))
+ return false;
+ return true;
+}
+
+/*
+ * Helper function to find the first entry of the next per-cpu list
+ * It works somewhat like for_each_possible_cpu(cpu).
+ *
+ * Return: true if the entry is found, false if all the lists exhausted
+ */
+static __always_inline bool
+__pcpu_list_next_cpu(struct pcpu_list_head *head, struct pcpu_list_state *state)
+{
+ if (state->lock)
+ spin_unlock(state->lock);
+next_cpu:
+ /*
+ * for_each_possible_cpu(cpu)
+ */
+ state->cpu = cpumask_next(state->cpu, cpu_possible_mask);
+ if (state->cpu >= nr_cpu_ids)
+ return false; /* All the per-cpu lists iterated */
+
+ state->head = &per_cpu_ptr(head, state->cpu)->list;
+ if (list_empty(state->head))
+ goto next_cpu;
+
+ state->lock = &per_cpu_ptr(head, state->cpu)->lock;
+ spin_lock(state->lock);
+ /*
+ * There is a slight chance that the list may become empty just
+ * before the lock is acquired. So an additional check is
+ * needed to make sure that state->curr points to a valid entry.
+ */
+ if (list_empty(state->head)) {
+ spin_unlock(state->lock);
+ goto next_cpu;
+ }
+ state->curr = list_entry(state->head->next,
+ struct pcpu_list_node, list);
+ return true;
+}
+
+/*
+ * Iterate to the next entry of the group of per-cpu lists
+ *
+ * Return: true if the next entry is found, false if all the entries iterated
+ */
+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);
+
+ if (!state->curr || (&state->curr->list == state->head)) {
+ /*
+ * The current per-cpu list has been exhausted, try the next
+ * per-cpu list.
+ */
+ if (!__pcpu_list_next_cpu(head, state))
+ return false;
+ }
+
+ PERCPU_LIST_WARN_ON(state->curr->lockptr != state->lock);
+ return true; /* Continue the iteration */
+}
+
+/*
+ * Iterate to the next entry of the group of per-cpu lists and safe
+ * against removal of list_entry
+ *
+ * Return: true if the next entry is found, false if all the entries iterated
+ */
+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);
+ }
+
+ if (!state->curr || (&state->curr->list == state->head)) {
+ /*
+ * The current per-cpu list has been exhausted, try the next
+ * per-cpu list.
+ */
+ if (!__pcpu_list_next_cpu(head, state))
+ return false;
+ state->next = list_next_entry(state->curr, list);
+ }
+
+ PERCPU_LIST_WARN_ON(state->curr->lockptr != state->lock);
+ return true; /* Continue the iteration */
+}
+
+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 int init_pcpu_list_head(struct pcpu_list_head **ppcpu_head);
+
+#endif /* __LINUX_PERCPU_LIST_H */
diff --git a/lib/Makefile b/lib/Makefile
index a65e9a8..387ed2b 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -40,7 +40,7 @@ obj-y += bcd.o div64.o sort.o parser.o halfmd4.o debug_locks.o random32.o \
gcd.o lcm.o list_sort.o uuid.o flex_array.o iov_iter.o clz_ctz.o \
bsearch.o find_bit.o llist.o memweight.o kfifo.o \
percpu-refcount.o percpu_ida.o rhashtable.o reciprocal_div.o \
- once.o
+ once.o percpu-list.o
obj-y += string_helpers.o
obj-$(CONFIG_TEST_STRING_HELPERS) += test-string_helpers.o
obj-y += hexdump.o
diff --git a/lib/percpu-list.c b/lib/percpu-list.c
new file mode 100644
index 0000000..8a96001
--- /dev/null
+++ b/lib/percpu-list.c
@@ -0,0 +1,100 @@
+/*
+ * Per-cpu list
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * (C) Copyright 2016 Hewlett-Packard Enterprise Development LP
+ *
+ * Authors: Waiman Long <waiman.long@hpe.com>
+ */
+#include <linux/percpu-list.h>
+#include <linux/lockdep.h>
+
+/*
+ * The per-cpu list lock needs its own class to avoid warning and stack
+ * trace when lockdep is enabled.
+ */
+static struct lock_class_key percpu_list_key;
+
+/*
+ * Initialize the per-cpu list head
+ */
+int init_pcpu_list_head(struct pcpu_list_head **ppcpu_head)
+{
+ struct pcpu_list_head *pcpu_head = alloc_percpu(struct pcpu_list_head);
+ int cpu;
+
+ if (!pcpu_head)
+ return -ENOMEM;
+
+ for_each_possible_cpu(cpu) {
+ struct pcpu_list_head *head = per_cpu_ptr(pcpu_head, cpu);
+
+ INIT_LIST_HEAD(&head->list);
+ head->lock = __SPIN_LOCK_UNLOCKED(&head->lock);
+ lockdep_set_class(&head->lock, &percpu_list_key);
+ }
+
+ *ppcpu_head = pcpu_head;
+ return 0;
+}
+
+/*
+ * List selection is based on the CPU being used when the pcpu_list_add()
+ * function is called. However, deletion may be done by a different CPU.
+ * So we still need to use a lock to protect the content of the list.
+ */
+void pcpu_list_add(struct pcpu_list_node *node, struct pcpu_list_head *head)
+{
+ struct pcpu_list_head *myhead;
+
+ /*
+ * Disable preemption to make sure that CPU won't gets changed.
+ */
+ preempt_disable();
+ myhead = this_cpu_ptr(head);
+ spin_lock(&myhead->lock);
+ node->lockptr = &myhead->lock;
+ list_add(&node->list, &myhead->list);
+ spin_unlock(&myhead->lock);
+ preempt_enable();
+}
+
+/*
+ * Delete a node from a percpu list
+ *
+ * We need to check the lock pointer again after taking the lock to guard
+ * against concurrent delete of the same node. If the lock pointer changes
+ * (becomes NULL or to a different one), we assume that the deletion was done
+ * elsewhere.
+ */
+void pcpu_list_del(struct pcpu_list_node *node)
+{
+ spinlock_t *lock = READ_ONCE(node->lockptr);
+
+ if (unlikely(!lock)) {
+ WARN(1, "pcpu_list_del: node 0x%lx has no associated lock\n",
+ (unsigned long)node);
+ return;
+ }
+
+ spin_lock(lock);
+ if (likely(lock == node->lockptr)) {
+ list_del_init(&node->list);
+ node->lockptr = NULL;
+ } else {
+ /*
+ * This path should never be executed.
+ */
+ WARN_ON(1);
+ }
+ spin_unlock(lock);
+}
--
1.7.1
\
 
 \ /
  Last update: 2016-04-13 01:21    [W:0.387 / U:0.064 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site