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Date: Fri, 11 Oct 2013 13:31:52 -0700
From: Kent Overstreet <kmo@...erainc.com>
To: Shaohua Li <shli@...nel.org>
Cc: linux-kernel@...r.kernel.org, axboe@...nel.dk
Subject: Re: [patch 1/4] percpu_ida: make percpu_ida percpu size/batch
configurable
On Fri, Oct 11, 2013 at 03:18:03PM +0800, Shaohua Li wrote:
> Make percpu_ida percpu size/batch configurable. The block-mq-tag will use it.
Can you explain the justification for this? Performance...?
> Signed-off-by: Shaohua Li <shli@...ionio.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 12:14:44.472699999 +0800
> +++ master/include/linux/percpu_ida.h 2013-10-11 12:14:44.472699999 +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 12:14:44.472699999 +0800
> +++ master/lib/percpu_ida.c 2013-10-11 12:14:44.472699999 +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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