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Subject[patch 1/4 v2] percpu_ida: make percpu_ida percpu size/batch configurable
Make percpu_ida percpu size/batch configurable. The block-mq-tag will use it.

After block-mq uses percpu_ida to manage tags, performance is improved. My test
is done in a 2 sockets machine, 12 process cross the 2 sockets. So if there is
lock contention or ipi, should be stressed heavily. Testing is done for
null-blk.

hw_queue_depth nopatch iops patch iops
64 ~800k/s ~1470k/s
2048 ~4470k/s ~4340k/s

Signed-off-by: Shaohua Li <shli@fusionio.com>
---
include/linux/percpu_ida.h | 18 +++++++++++++++++-
lib/percpu_ida.c | 28 +++++++++++-----------------
2 files changed, 28 insertions(+), 18 deletions(-)

Index: master/include/linux/percpu_ida.h
===================================================================
--- master.orig/include/linux/percpu_ida.h 2013-10-11 14:34:40.367149789 +0800
+++ master/include/linux/percpu_ida.h 2013-10-15 08:24:39.000000000 +0800
@@ -16,6 +16,8 @@ struct percpu_ida {
* percpu_ida_init()
*/
unsigned nr_tags;
+ unsigned percpu_max_size;
+ unsigned percpu_batch_size;

struct percpu_ida_cpu __percpu *tag_cpu;

@@ -51,10 +53,24 @@ struct percpu_ida {
} ____cacheline_aligned_in_smp;
};

+/*
+ * Number of tags we move between the percpu freelist and the global freelist at
+ * a time
+ */
+#define IDA_DEFAULT_PCPU_BATCH_MOVE 32U
+/* Max size of percpu freelist, */
+#define IDA_DEFAULT_PCPU_SIZE ((IDA_DEFAULT_PCPU_BATCH_MOVE * 3) / 2)
+
int percpu_ida_alloc(struct percpu_ida *pool, gfp_t gfp);
void percpu_ida_free(struct percpu_ida *pool, unsigned tag);

void percpu_ida_destroy(struct percpu_ida *pool);
-int percpu_ida_init(struct percpu_ida *pool, unsigned long nr_tags);
+int __percpu_ida_init(struct percpu_ida *pool, unsigned long nr_tags,
+ unsigned long max_size, unsigned long batch_size);
+static inline int percpu_ida_init(struct percpu_ida *pool, unsigned long nr_tags)
+{
+ return __percpu_ida_init(pool, nr_tags, IDA_DEFAULT_PCPU_SIZE,
+ IDA_DEFAULT_PCPU_BATCH_MOVE);
+}

#endif /* __PERCPU_IDA_H__ */
Index: master/lib/percpu_ida.c
===================================================================
--- master.orig/lib/percpu_ida.c 2013-10-11 14:34:40.367149789 +0800
+++ master/lib/percpu_ida.c 2013-10-15 08:24:39.000000000 +0800
@@ -30,15 +30,6 @@
#include <linux/spinlock.h>
#include <linux/percpu_ida.h>

-/*
- * Number of tags we move between the percpu freelist and the global freelist at
- * a time
- */
-#define IDA_PCPU_BATCH_MOVE 32U
-
-/* Max size of percpu freelist, */
-#define IDA_PCPU_SIZE ((IDA_PCPU_BATCH_MOVE * 3) / 2)
-
struct percpu_ida_cpu {
/*
* Even though this is percpu, we need a lock for tag stealing by remote
@@ -78,7 +69,7 @@ static inline void steal_tags(struct per
struct percpu_ida_cpu *remote;

for (cpus_have_tags = cpumask_weight(&pool->cpus_have_tags);
- cpus_have_tags * IDA_PCPU_SIZE > pool->nr_tags / 2;
+ cpus_have_tags * pool->percpu_max_size > pool->nr_tags / 2;
cpus_have_tags--) {
cpu = cpumask_next(cpu, &pool->cpus_have_tags);

@@ -123,7 +114,7 @@ static inline void alloc_global_tags(str
{
move_tags(tags->freelist, &tags->nr_free,
pool->freelist, &pool->nr_free,
- min(pool->nr_free, IDA_PCPU_BATCH_MOVE));
+ min(pool->nr_free, pool->percpu_batch_size));
}

static inline unsigned alloc_local_tag(struct percpu_ida *pool,
@@ -245,17 +236,17 @@ void percpu_ida_free(struct percpu_ida *
wake_up(&pool->wait);
}

- if (nr_free == IDA_PCPU_SIZE) {
+ if (nr_free == pool->percpu_max_size) {
spin_lock(&pool->lock);

/*
* Global lock held and irqs disabled, don't need percpu
* lock
*/
- if (tags->nr_free == IDA_PCPU_SIZE) {
+ if (tags->nr_free == pool->percpu_max_size) {
move_tags(pool->freelist, &pool->nr_free,
tags->freelist, &tags->nr_free,
- IDA_PCPU_BATCH_MOVE);
+ pool->percpu_batch_size);

wake_up(&pool->wait);
}
@@ -292,7 +283,8 @@ EXPORT_SYMBOL_GPL(percpu_ida_destroy);
* Allocation is percpu, but sharding is limited by nr_tags - for best
* performance, the workload should not span more cpus than nr_tags / 128.
*/
-int percpu_ida_init(struct percpu_ida *pool, unsigned long nr_tags)
+int __percpu_ida_init(struct percpu_ida *pool, unsigned long nr_tags,
+ unsigned long max_size, unsigned long batch_size)
{
unsigned i, cpu, order;

@@ -301,6 +293,8 @@ int percpu_ida_init(struct percpu_ida *p
init_waitqueue_head(&pool->wait);
spin_lock_init(&pool->lock);
pool->nr_tags = nr_tags;
+ pool->percpu_max_size = max_size;
+ pool->percpu_batch_size = batch_size;

/* Guard against overflow */
if (nr_tags > (unsigned) INT_MAX + 1) {
@@ -319,7 +313,7 @@ int percpu_ida_init(struct percpu_ida *p
pool->nr_free = nr_tags;

pool->tag_cpu = __alloc_percpu(sizeof(struct percpu_ida_cpu) +
- IDA_PCPU_SIZE * sizeof(unsigned),
+ pool->percpu_max_size * sizeof(unsigned),
sizeof(unsigned));
if (!pool->tag_cpu)
goto err;
@@ -332,4 +326,4 @@ err:
percpu_ida_destroy(pool);
return -ENOMEM;
}
-EXPORT_SYMBOL_GPL(percpu_ida_init);
+EXPORT_SYMBOL_GPL(__percpu_ida_init);


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