linux/lib/percpu_ida.c
Shaohua Li 1dddc01af0 percpu_ida: add an API to return free tags
Add an API to return free tags, blk-mq-tag will use it.

Note, this just returns a snapshot of free tags number. blk-mq-tag has
two usages of it. One is for info output for diagnosis. The other is to
quickly check if there are free tags for request dispatch checking.
Neither requires very precise.

Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Shaohua Li <shli@fusionio.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2013-10-25 11:56:00 +01:00

391 lines
9.6 KiB
C

/*
* Percpu IDA library
*
* Copyright (C) 2013 Datera, Inc. Kent Overstreet
*
* 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, 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.
*/
#include <linux/bitmap.h>
#include <linux/bitops.h>
#include <linux/bug.h>
#include <linux/err.h>
#include <linux/export.h>
#include <linux/hardirq.h>
#include <linux/idr.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/percpu.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/string.h>
#include <linux/spinlock.h>
#include <linux/percpu_ida.h>
struct percpu_ida_cpu {
/*
* Even though this is percpu, we need a lock for tag stealing by remote
* CPUs:
*/
spinlock_t lock;
/* nr_free/freelist form a stack of free IDs */
unsigned nr_free;
unsigned freelist[];
};
static inline void move_tags(unsigned *dst, unsigned *dst_nr,
unsigned *src, unsigned *src_nr,
unsigned nr)
{
*src_nr -= nr;
memcpy(dst + *dst_nr, src + *src_nr, sizeof(unsigned) * nr);
*dst_nr += nr;
}
/*
* Try to steal tags from a remote cpu's percpu freelist.
*
* We first check how many percpu freelists have tags - we don't steal tags
* unless enough percpu freelists have tags on them that it's possible more than
* half the total tags could be stuck on remote percpu freelists.
*
* Then we iterate through the cpus until we find some tags - we don't attempt
* to find the "best" cpu to steal from, to keep cacheline bouncing to a
* minimum.
*/
static inline void steal_tags(struct percpu_ida *pool,
struct percpu_ida_cpu *tags)
{
unsigned cpus_have_tags, cpu = pool->cpu_last_stolen;
struct percpu_ida_cpu *remote;
for (cpus_have_tags = cpumask_weight(&pool->cpus_have_tags);
cpus_have_tags * pool->percpu_max_size > pool->nr_tags / 2;
cpus_have_tags--) {
cpu = cpumask_next(cpu, &pool->cpus_have_tags);
if (cpu >= nr_cpu_ids) {
cpu = cpumask_first(&pool->cpus_have_tags);
if (cpu >= nr_cpu_ids)
BUG();
}
pool->cpu_last_stolen = cpu;
remote = per_cpu_ptr(pool->tag_cpu, cpu);
cpumask_clear_cpu(cpu, &pool->cpus_have_tags);
if (remote == tags)
continue;
spin_lock(&remote->lock);
if (remote->nr_free) {
memcpy(tags->freelist,
remote->freelist,
sizeof(unsigned) * remote->nr_free);
tags->nr_free = remote->nr_free;
remote->nr_free = 0;
}
spin_unlock(&remote->lock);
if (tags->nr_free)
break;
}
}
/*
* Pop up to IDA_PCPU_BATCH_MOVE IDs off the global freelist, and push them onto
* our percpu freelist:
*/
static inline void alloc_global_tags(struct percpu_ida *pool,
struct percpu_ida_cpu *tags)
{
move_tags(tags->freelist, &tags->nr_free,
pool->freelist, &pool->nr_free,
min(pool->nr_free, pool->percpu_batch_size));
}
static inline unsigned alloc_local_tag(struct percpu_ida *pool,
struct percpu_ida_cpu *tags)
{
int tag = -ENOSPC;
spin_lock(&tags->lock);
if (tags->nr_free)
tag = tags->freelist[--tags->nr_free];
spin_unlock(&tags->lock);
return tag;
}
/**
* percpu_ida_alloc - allocate a tag
* @pool: pool to allocate from
* @gfp: gfp flags
*
* Returns a tag - an integer in the range [0..nr_tags) (passed to
* tag_pool_init()), or otherwise -ENOSPC on allocation failure.
*
* Safe to be called from interrupt context (assuming it isn't passed
* __GFP_WAIT, of course).
*
* @gfp indicates whether or not to wait until a free id is available (it's not
* used for internal memory allocations); thus if passed __GFP_WAIT we may sleep
* however long it takes until another thread frees an id (same semantics as a
* mempool).
*
* Will not fail if passed __GFP_WAIT.
*/
int percpu_ida_alloc(struct percpu_ida *pool, gfp_t gfp)
{
DEFINE_WAIT(wait);
struct percpu_ida_cpu *tags;
unsigned long flags;
int tag;
local_irq_save(flags);
tags = this_cpu_ptr(pool->tag_cpu);
/* Fastpath */
tag = alloc_local_tag(pool, tags);
if (likely(tag >= 0)) {
local_irq_restore(flags);
return tag;
}
while (1) {
spin_lock(&pool->lock);
/*
* prepare_to_wait() must come before steal_tags(), in case
* percpu_ida_free() on another cpu flips a bit in
* cpus_have_tags
*
* global lock held and irqs disabled, don't need percpu lock
*/
prepare_to_wait(&pool->wait, &wait, TASK_UNINTERRUPTIBLE);
if (!tags->nr_free)
alloc_global_tags(pool, tags);
if (!tags->nr_free)
steal_tags(pool, tags);
if (tags->nr_free) {
tag = tags->freelist[--tags->nr_free];
if (tags->nr_free)
cpumask_set_cpu(smp_processor_id(),
&pool->cpus_have_tags);
}
spin_unlock(&pool->lock);
local_irq_restore(flags);
if (tag >= 0 || !(gfp & __GFP_WAIT))
break;
schedule();
local_irq_save(flags);
tags = this_cpu_ptr(pool->tag_cpu);
}
finish_wait(&pool->wait, &wait);
return tag;
}
EXPORT_SYMBOL_GPL(percpu_ida_alloc);
/**
* percpu_ida_free - free a tag
* @pool: pool @tag was allocated from
* @tag: a tag previously allocated with percpu_ida_alloc()
*
* Safe to be called from interrupt context.
*/
void percpu_ida_free(struct percpu_ida *pool, unsigned tag)
{
struct percpu_ida_cpu *tags;
unsigned long flags;
unsigned nr_free;
BUG_ON(tag >= pool->nr_tags);
local_irq_save(flags);
tags = this_cpu_ptr(pool->tag_cpu);
spin_lock(&tags->lock);
tags->freelist[tags->nr_free++] = tag;
nr_free = tags->nr_free;
spin_unlock(&tags->lock);
if (nr_free == 1) {
cpumask_set_cpu(smp_processor_id(),
&pool->cpus_have_tags);
wake_up(&pool->wait);
}
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 == pool->percpu_max_size) {
move_tags(pool->freelist, &pool->nr_free,
tags->freelist, &tags->nr_free,
pool->percpu_batch_size);
wake_up(&pool->wait);
}
spin_unlock(&pool->lock);
}
local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(percpu_ida_free);
/**
* percpu_ida_destroy - release a tag pool's resources
* @pool: pool to free
*
* Frees the resources allocated by percpu_ida_init().
*/
void percpu_ida_destroy(struct percpu_ida *pool)
{
free_percpu(pool->tag_cpu);
free_pages((unsigned long) pool->freelist,
get_order(pool->nr_tags * sizeof(unsigned)));
}
EXPORT_SYMBOL_GPL(percpu_ida_destroy);
/**
* percpu_ida_init - initialize a percpu tag pool
* @pool: pool to initialize
* @nr_tags: number of tags that will be available for allocation
*
* Initializes @pool so that it can be used to allocate tags - integers in the
* range [0, nr_tags). Typically, they'll be used by driver code to refer to a
* preallocated array of tag structures.
*
* 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,
unsigned long max_size, unsigned long batch_size)
{
unsigned i, cpu, order;
memset(pool, 0, sizeof(*pool));
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) {
pr_err("percpu_ida_init(): nr_tags too large\n");
return -EINVAL;
}
order = get_order(nr_tags * sizeof(unsigned));
pool->freelist = (void *) __get_free_pages(GFP_KERNEL, order);
if (!pool->freelist)
return -ENOMEM;
for (i = 0; i < nr_tags; i++)
pool->freelist[i] = i;
pool->nr_free = nr_tags;
pool->tag_cpu = __alloc_percpu(sizeof(struct percpu_ida_cpu) +
pool->percpu_max_size * sizeof(unsigned),
sizeof(unsigned));
if (!pool->tag_cpu)
goto err;
for_each_possible_cpu(cpu)
spin_lock_init(&per_cpu_ptr(pool->tag_cpu, cpu)->lock);
return 0;
err:
percpu_ida_destroy(pool);
return -ENOMEM;
}
EXPORT_SYMBOL_GPL(__percpu_ida_init);
/**
* percpu_ida_for_each_free - iterate free ids of a pool
* @pool: pool to iterate
* @fn: interate callback function
* @data: parameter for @fn
*
* Note, this doesn't guarantee to iterate all free ids restrictly. Some free
* ids might be missed, some might be iterated duplicated, and some might
* be iterated and not free soon.
*/
int percpu_ida_for_each_free(struct percpu_ida *pool, percpu_ida_cb fn,
void *data)
{
unsigned long flags;
struct percpu_ida_cpu *remote;
unsigned cpu, i, err = 0;
local_irq_save(flags);
for_each_possible_cpu(cpu) {
remote = per_cpu_ptr(pool->tag_cpu, cpu);
spin_lock(&remote->lock);
for (i = 0; i < remote->nr_free; i++) {
err = fn(remote->freelist[i], data);
if (err)
break;
}
spin_unlock(&remote->lock);
if (err)
goto out;
}
spin_lock(&pool->lock);
for (i = 0; i < pool->nr_free; i++) {
err = fn(pool->freelist[i], data);
if (err)
break;
}
spin_unlock(&pool->lock);
out:
local_irq_restore(flags);
return err;
}
EXPORT_SYMBOL_GPL(percpu_ida_for_each_free);
/**
* percpu_ida_free_tags - return free tags number of a specific cpu or global pool
* @pool: pool related
* @cpu: specific cpu or global pool if @cpu == nr_cpu_ids
*
* Note: this just returns a snapshot of free tags number.
*/
unsigned percpu_ida_free_tags(struct percpu_ida *pool, int cpu)
{
struct percpu_ida_cpu *remote;
if (cpu == nr_cpu_ids)
return pool->nr_free;
remote = per_cpu_ptr(pool->tag_cpu, cpu);
return remote->nr_free;
}
EXPORT_SYMBOL_GPL(percpu_ida_free_tags);