diff options
Diffstat (limited to 'lib')
| -rw-r--r-- | lib/Makefile | 5 | ||||
| -rw-r--r-- | lib/percpu_ida.c | 335 |
2 files changed, 338 insertions, 2 deletions
diff --git a/lib/Makefile b/lib/Makefile index f2cb3082697..f3bb2cb98ad 100644 --- a/lib/Makefile +++ b/lib/Makefile @@ -13,7 +13,7 @@ lib-y := ctype.o string.o vsprintf.o cmdline.o \ sha1.o md5.o irq_regs.o reciprocal_div.o argv_split.o \ proportions.o flex_proportions.o prio_heap.o ratelimit.o show_mem.o \ is_single_threaded.o plist.o decompress.o kobject_uevent.o \ - earlycpio.o percpu-refcount.o + earlycpio.o percpu-refcount.o percpu_ida.o obj-$(CONFIG_ARCH_HAS_DEBUG_STRICT_USER_COPY_CHECKS) += usercopy.o lib-$(CONFIG_MMU) += ioremap.o @@ -25,7 +25,8 @@ obj-y += lockref.o obj-y += bcd.o div64.o sort.o parser.o halfmd4.o debug_locks.o random32.o \ bust_spinlocks.o hexdump.o kasprintf.o bitmap.o scatterlist.o \ gcd.o lcm.o list_sort.o uuid.o flex_array.o iovec.o clz_ctz.o \ - bsearch.o find_last_bit.o find_next_bit.o llist.o memweight.o kfifo.o + bsearch.o find_last_bit.o find_next_bit.o llist.o memweight.o kfifo.o \ + percpu_ida.o obj-y += string_helpers.o obj-$(CONFIG_TEST_STRING_HELPERS) += test-string_helpers.o obj-y += kstrtox.o diff --git a/lib/percpu_ida.c b/lib/percpu_ida.c new file mode 100644 index 00000000000..bab1ba2a4c7 --- /dev/null +++ b/lib/percpu_ida.c @@ -0,0 +1,335 @@ +/* + * 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> + +/* + * 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 + * 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 * IDA_PCPU_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, IDA_PCPU_BATCH_MOVE)); +} + +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 == IDA_PCPU_SIZE) { + spin_lock(&pool->lock); + + /* + * Global lock held and irqs disabled, don't need percpu + * lock + */ + if (tags->nr_free == IDA_PCPU_SIZE) { + move_tags(pool->freelist, &pool->nr_free, + tags->freelist, &tags->nr_free, + IDA_PCPU_BATCH_MOVE); + + 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 i, cpu, order; + + memset(pool, 0, sizeof(*pool)); + + init_waitqueue_head(&pool->wait); + spin_lock_init(&pool->lock); + pool->nr_tags = nr_tags; + + /* 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) + + IDA_PCPU_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); |