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Subject[PATCH 1/2] tmpfs: Quick token library to allow scalable retrieval of tokens from token jar
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This patch creates a quick token (qtoken) library to maintain local
caches of tokens. This avoids lock contention when a token is
retrieved or returned to the token jar, and allows better scaling
on system with many cpus.

Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
include/linux/qtoken.h | 40 ++++++++
lib/Makefile | 2 +-
lib/qtoken.c | 235 ++++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 276 insertions(+), 1 deletions(-)

diff --git a/include/linux/qtoken.h b/include/linux/qtoken.h
new file mode 100644
index 0000000..a09bba9
--- /dev/null
+++ b/include/linux/qtoken.h
@@ -0,0 +1,40 @@
+/*
+ * qtoken.h: Structure and function prototypes to implement quick token
+ * retrieval from a jar of tokens with per cpu cache.
+ *
+ * Copyright (C) 2010 Intel Corporation
+ * Author: Tim Chen <tim.c.chen@linux.intel.com>
+ *
+ * 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; version 2
+ * of the License.
+ *
+ */
+
+#ifndef _QTOKEN_H
+#define _QTOKEN_H
+
+#define QTOKEN_CACHE_HIGHMARK 2
+#define QTOKEN_POOL_HIGHMARK (2 * QTOKEN_CACHE_HIGHMARK)
+
+struct qtoken {
+ long pool; /* pool of free tokens */
+ long total; /* total num of tokens */
+#ifdef CONFIG_SMP
+ long init_cache_sz; /* initial cache size */
+ spinlock_t lock; /* lock on token jar */
+ atomic_long_t __percpu *cache; /* per cpu cache of tokens */
+#endif
+};
+
+extern void qtoken_return(struct qtoken *token_jar, long tokens);
+extern int qtoken_get(struct qtoken *token_jar, long tkn, long reserve);
+extern int qtoken_init(struct qtoken *token_jar, long total_tokens,
+ long init_cache_sz);
+extern void qtoken_put(struct qtoken *token_jar);
+extern long qtoken_avail(struct qtoken *token_jar);
+extern int qtoken_resize(struct qtoken *token_jar, long new_total_tokens);
+extern long qtoken_total(struct qtoken *token_jar);
+
+#endif /* _QTOKEN_H */
diff --git a/lib/Makefile b/lib/Makefile
index 0d40152..1fa8945 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -12,7 +12,7 @@ lib-y := ctype.o string.o vsprintf.o cmdline.o \
idr.o int_sqrt.o extable.o prio_tree.o \
sha1.o irq_regs.o reciprocal_div.o argv_split.o \
proportions.o prio_heap.o ratelimit.o show_mem.o \
- is_single_threaded.o plist.o decompress.o flex_array.o
+ is_single_threaded.o plist.o decompress.o flex_array.o qtoken.o

lib-$(CONFIG_MMU) += ioremap.o
lib-$(CONFIG_SMP) += cpumask.o
diff --git a/lib/qtoken.c b/lib/qtoken.c
new file mode 100644
index 0000000..9ab34f2
--- /dev/null
+++ b/lib/qtoken.c
@@ -0,0 +1,235 @@
+/*
+ * qtoken.c: Library of functions to implement quick token
+ * retrieval from a jar of tokens with per cpu cache.
+ *
+ * Copyright (C) 2010 Intel Corporation
+ * Author: Tim Chen <tim.c.chen@linux.intel.com>
+ *
+ * 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; version 2
+ * of the License.
+ *
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/cpumask.h>
+#include <linux/qtoken.h>
+
+void qtoken_return(struct qtoken *token_jar, long tokens)
+{
+#ifdef CONFIG_SMP
+ long cnt;
+ int cpu;
+ atomic_long_t *cache;
+
+ cpu = get_cpu();
+ cache = per_cpu_ptr(token_jar->cache, cpu);
+ cnt = atomic_long_read(cache);
+ if (cnt >= 0) {
+ if (likely((cnt+tokens) <=
+ QTOKEN_CACHE_HIGHMARK*token_jar->init_cache_sz)) {
+ /* Add freed tokens to local cache unless cache was
+ * reaped and disabled, return tokens to pool
+ * for that case
+ */
+ if (!atomic_long_add_unless(
+ cache, tokens, -1)) {
+ spin_lock(&token_jar->lock);
+ token_jar->pool += tokens;
+ spin_unlock(&token_jar->lock);
+ }
+ } else {
+ spin_lock(&token_jar->lock);
+ /* If cache has not been reaped and set to -1,
+ * set cache to init cache size
+ */
+ if (atomic_long_add_unless(
+ cache, token_jar->init_cache_sz-cnt, -1)) {
+ long excess = cnt + tokens -
+ token_jar->init_cache_sz;
+
+ token_jar->pool += excess;
+ } else
+ token_jar->pool += tokens;
+ spin_unlock(&token_jar->lock);
+ }
+ } else {
+ /* local cache reaped and disabled, */
+ /* return pages to global pool */
+ spin_lock(&token_jar->lock);
+ token_jar->pool += tokens;
+ spin_unlock(&token_jar->lock);
+ }
+ put_cpu();
+#else
+ token_jar->pool += tokens;
+#endif
+}
+EXPORT_SYMBOL(qtoken_return);
+
+#ifdef CONFIG_SMP
+static void qtoken_reap_cache(struct qtoken *token_jar)
+{
+ long cnt;
+ int i;
+
+ /* Need to have already acquired lock before here */
+ /* Reap cache into pool and disable local cache */
+ for_each_possible_cpu(i) {
+ atomic_long_t *cache;
+
+ cache = per_cpu_ptr(token_jar->cache, i);
+ cnt = atomic_long_xchg(cache, -1);
+ if (cnt > 0)
+ token_jar->pool += cnt;
+ }
+}
+#endif
+
+static int qtoken_from_pool(struct qtoken *token_jar, unsigned tkn,
+ unsigned reserve)
+{
+ int allocated = 0;
+
+#ifdef CONFIG_SMP
+ /* Need to have acquired lock of token pool before coming here */
+ if (token_jar->pool < (reserve+tkn))
+ qtoken_reap_cache(token_jar);
+#endif
+ if (token_jar->pool >= (reserve+tkn)) {
+ token_jar->pool -= tkn;
+ allocated = 1;
+ }
+ return allocated;
+}
+
+int qtoken_get(struct qtoken *token_jar, long tkn, long reserve)
+{
+ int allocated = 0;
+#ifdef CONFIG_SMP
+ int cpu;
+ long cnt;
+ atomic_long_t *cache;
+
+ if (tkn <= 0)
+ return 0;
+ cpu = get_cpu();
+ cache = per_cpu_ptr(token_jar->cache, cpu);
+ cnt = atomic_long_read(cache);
+ /* Need to reserve tokens after allocation */
+ if ((cnt > reserve) && (cnt >= tkn)) {
+ if (atomic_long_add_unless(cache, -tkn, -1))
+ allocated = 1;
+ else {
+ /* cache has been reaped, get token from pool */
+ spin_lock(&token_jar->lock);
+ allocated = qtoken_from_pool(token_jar, tkn, reserve);
+ spin_unlock(&token_jar->lock);
+ }
+ } else {
+ /* cache low, allocate from pool */
+ spin_lock(&token_jar->lock);
+ if ((token_jar->pool - tkn) > (QTOKEN_POOL_HIGHMARK *
+ token_jar->init_cache_sz * num_possible_cpus())) {
+ /* abundant tokens in pool */
+ /* allocate token and replenish cache */
+ token_jar->pool -= tkn;
+ allocated = tkn;
+ token_jar->pool -= token_jar->init_cache_sz;
+ cnt = atomic_long_read(cache);
+ if (cnt < 0)
+ cnt = token_jar->init_cache_sz;
+ else
+ cnt += token_jar->init_cache_sz;
+ atomic_long_set(cache, cnt);
+ } else
+ allocated = qtoken_from_pool(token_jar, tkn, reserve);
+ spin_unlock(&token_jar->lock);
+ }
+ put_cpu();
+#else
+ allocated = qtoken_from_pool(token_jar, tkn, reserve);
+#endif
+ return allocated;
+}
+EXPORT_SYMBOL(qtoken_get);
+
+int qtoken_init(struct qtoken *token_jar, long total_tokens, long cache_size)
+{
+#ifdef CONFIG_SMP
+ int i;
+
+ token_jar->cache = alloc_percpu(atomic_long_t);
+ if (!token_jar->cache)
+ return 0;
+ spin_lock_init(&token_jar->lock);
+ for_each_possible_cpu(i) {
+ atomic_long_t *cache;
+
+ cache = per_cpu_ptr(token_jar->cache, i);
+ atomic_long_set(cache, -1);
+ }
+ token_jar->init_cache_sz = cache_size;
+#endif
+ token_jar->total = token_jar->pool = total_tokens;
+ return 1;
+}
+EXPORT_SYMBOL(qtoken_init);
+
+void qtoken_put(struct qtoken *token_jar)
+{
+#ifdef CONFIG_SMP
+ if (token_jar->cache)
+ free_percpu(token_jar->cache);
+#endif
+ token_jar->pool = 0;
+ token_jar->total = 0;
+}
+EXPORT_SYMBOL(qtoken_put);
+
+/* This function should be called sparingly, it is
+ * expensive to get a total count of free tokens.
+ */
+long qtoken_avail(struct qtoken *token_jar)
+{
+ long cnt;
+
+#ifdef CONFIG_SMP
+ spin_lock(&token_jar->lock);
+ qtoken_reap_cache(token_jar);
+ cnt = token_jar->pool;
+ spin_unlock(&token_jar->lock);
+#else
+ cnt = token_jar->pool;
+#endif
+ return cnt;
+}
+EXPORT_SYMBOL(qtoken_avail);
+
+int qtoken_resize(struct qtoken *token_jar, long new_total_tokens)
+{
+ long in_use;
+
+#ifdef CONFIG_SMP
+ spin_lock(&token_jar->lock);
+ qtoken_reap_cache(token_jar);
+#endif
+ in_use = token_jar->total - token_jar->pool;
+ if (in_use > new_total_tokens)
+ return 0;
+ token_jar->total = new_total_tokens - in_use;
+#ifdef CONFIG_SMP
+ spin_unlock(&token_jar->lock);
+#endif
+ return 1;
+}
+EXPORT_SYMBOL(qtoken_resize);
+
+long qtoken_total(struct qtoken *token_jar)
+{
+ return token_jar->total;
+}
+EXPORT_SYMBOL(qtoken_total);



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