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/* SPDX-License-Identifier: GPL-2.0-or-later / / * Definitions for the 'struct ptr_ring' datastructure. * * Author: * Michael S. Tsirkin <mst@redhat.com> * * Copyright (C) 2016 Red Hat, Inc. * * This is a limited-size FIFO maintaining pointers in FIFO order, with * one CPU producing entries and another consuming entries from a FIFO. * * This implementation tries to minimize cache-contention when there is a * single producer and a single consumer CPU. / #ifndef _LINUX_PTR_RING_H #define _LINUX_PTR_RING_H 1 #ifdef __KERNEL__ #include <linux/spinlock.h> #include <linux/cache.h> #include <linux/types.h> #include <linux/compiler.h> #include <linux/slab.h> #include <asm/errno.h> #endif struct ptr_ring { int producer ____cacheline_aligned_in_smp; spinlock_t producer_lock; int consumer_head ____cacheline_aligned_in_smp; / next valid entry / int consumer_tail; / next entry to invalidate / spinlock_t consumer_lock; / Shared consumer/producer data / / Read-only by both the producer and the consumer / int size ____cacheline_aligned_in_smp; / max entries in queue / int batch; / number of entries to consume in a batch / void queue; }; / Note: callers invoking this in a loop must use a compiler barrier, * for example cpu_relax(). * * NB: this is unlike __ptr_ring_empty in that callers must hold producer_lock: * see e.g. ptr_ring_full. / static inline bool __ptr_ring_full(struct ptr_ring r) { return r->queue[r->producer]; } static inline bool ptr_ring_full(struct ptr_ring r) { bool ret; spin_lock(&r->producer_lock); ret = __ptr_ring_full(r); spin_unlock(&r->producer_lock); return ret; } static inline bool ptr_ring_full_irq(struct ptr_ring r) { bool ret; spin_lock_irq(&r->producer_lock); ret = __ptr_ring_full(r); spin_unlock_irq(&r->producer_lock); return ret; } static inline bool ptr_ring_full_any(struct ptr_ring r) { unsigned long flags; bool ret; spin_lock_irqsave(&r->producer_lock, flags); ret = __ptr_ring_full(r); spin_unlock_irqrestore(&r->producer_lock, flags); return ret; } static inline bool ptr_ring_full_bh(struct ptr_ring r) { bool ret; spin_lock_bh(&r->producer_lock); ret = __ptr_ring_full(r); spin_unlock_bh(&r->producer_lock); return ret; } /* Note: callers invoking this in a loop must use a compiler barrier, * for example cpu_relax(). Callers must hold producer_lock. * Callers are responsible for making sure pointer that is being queued * points to a valid data. / static inline int __ptr_ring_produce(struct ptr_ring r, void ptr) { if (unlikely(!r->size) \|\| r->queue[r->producer]) return -ENOSPC; / Make sure the pointer we are storing points to a valid data. / / Pairs with smp_read_barrier_depends in __ptr_ring_consume. / smp_wmb(); WRITE_ONCE(r->queue[r->producer++], ptr); if (unlikely(r->producer >= r->size)) r->producer = 0; return 0; } / * Note: resize (below) nests producer lock within consumer lock, so if you * consume in interrupt or BH context, you must disable interrupts/BH when * calling this. / static inline int ptr_ring_produce(struct ptr_ring r, void ptr) { int ret; spin_lock(&r->producer_lock); ret = __ptr_ring_produce(r, ptr); spin_unlock(&r->producer_lock); return ret; } static inline int ptr_ring_produce_irq(struct ptr_ring r, void ptr) { int ret; spin_lock_irq(&r->producer_lock); ret = __ptr_ring_produce(r, ptr); spin_unlock_irq(&r->producer_lock); return ret; } static inline int ptr_ring_produce_any(struct ptr_ring r, void ptr) { unsigned long flags; int ret; spin_lock_irqsave(&r->producer_lock, flags); ret = __ptr_ring_produce(r, ptr); spin_unlock_irqrestore(&r->producer_lock, flags); return ret; } static inline int ptr_ring_produce_bh(struct ptr_ring r, void ptr) { int ret; spin_lock_bh(&r->producer_lock); ret = __ptr_ring_produce(r, ptr); spin_unlock_bh(&r->producer_lock); return ret; } static inline void __ptr_ring_peek(struct ptr_ring r) { if (likely(r->size)) return READ_ONCE(r->queue[r->consumer_head]); return NULL; } / * Test ring empty status without taking any locks. * * NB: This is only safe to call if ring is never resized. * * However, if some other CPU consumes ring entries at the same time, the value * returned is not guaranteed to be correct. * * In this case - to avoid incorrectly detecting the ring * as empty - the CPU consuming the ring entries is responsible * for either consuming all ring entries until the ring is empty, * or synchronizing with some other CPU and causing it to * re-test __ptr_ring_empty and/or consume the ring enteries * after the synchronization point. * * Note: callers invoking this in a loop must use a compiler barrier, * for example cpu_relax(). / static inline bool __ptr_ring_empty(struct ptr_ring r) { if (likely(r->size)) return !r->queue[READ_ONCE(r->consumer_head)]; return true; } static inline bool ptr_ring_empty(struct ptr_ring r) { bool ret; spin_lock(&r->consumer_lock); ret = __ptr_ring_empty(r); spin_unlock(&r->consumer_lock); return ret; } static inline bool ptr_ring_empty_irq(struct ptr_ring r) { bool ret; spin_lock_irq(&r->consumer_lock); ret = __ptr_ring_empty(r); spin_unlock_irq(&r->consumer_lock); return ret; } static inline bool ptr_ring_empty_any(struct ptr_ring r) { unsigned long flags; bool ret; spin_lock_irqsave(&r->consumer_lock, flags); ret = __ptr_ring_empty(r); spin_unlock_irqrestore(&r->consumer_lock, flags); return ret; } static inline bool ptr_ring_empty_bh(struct ptr_ring r) { bool ret; spin_lock_bh(&r->consumer_lock); ret = __ptr_ring_empty(r); spin_unlock_bh(&r->consumer_lock); return ret; } /* Must only be called after __ptr_ring_peek returned !NULL / static inline void __ptr_ring_discard_one(struct ptr_ring r) { /* Fundamentally, what we want to do is update consumer * index and zero out the entry so producer can reuse it. * Doing it naively at each consume would be as simple as: * consumer = r->consumer; * r->queue[consumer++] = NULL; * if (unlikely(consumer >= r->size)) * consumer = 0; * r->consumer = consumer; * but that is suboptimal when the ring is full as producer is writing * out new entries in the same cache line. Defer these updates until a * batch of entries has been consumed. / / Note: we must keep consumer_head valid at all times for __ptr_ring_empty * to work correctly. / int consumer_head = r->consumer_head; int head = consumer_head++; / Once we have processed enough entries invalidate them in * the ring all at once so producer can reuse their space in the ring. * We also do this when we reach end of the ring - not mandatory * but helps keep the implementation simple. / if (unlikely(consumer_head - r->consumer_tail >= r->batch \|\| consumer_head >= r->size)) { / Zero out entries in the reverse order: this way we touch the * cache line that producer might currently be reading the last; * producer won't make progress and touch other cache lines * besides the first one until we write out all entries. / while (likely(head >= r->consumer_tail)) r->queue[head--] = NULL; r->consumer_tail = consumer_head; } if (unlikely(consumer_head >= r->size)) { consumer_head = 0; r->consumer_tail = 0; } / matching READ_ONCE in __ptr_ring_empty for lockless tests / WRITE_ONCE(r->consumer_head, consumer_head); } static inline void __ptr_ring_consume(struct ptr_ring r) { void ptr; /* The READ_ONCE in __ptr_ring_peek guarantees that anyone * accessing data through the pointer is up to date. Pairs * with smp_wmb in __ptr_ring_produce. / ptr = __ptr_ring_peek(r); if (ptr) __ptr_ring_discard_one(r); return ptr; } static inline int __ptr_ring_consume_batched(struct ptr_ring r, void *array, int n) { void ptr; int i; for (i = 0; i < n; i++) { ptr = __ptr_ring_consume(r); if (!ptr) break; array[i] = ptr; } return i; } /* * Note: resize (below) nests producer lock within consumer lock, so if you * call this in interrupt or BH context, you must disable interrupts/BH when * producing. / static inline void ptr_ring_consume(struct ptr_ring r) { void ptr; spin_lock(&r->consumer_lock); ptr = __ptr_ring_consume(r); spin_unlock(&r->consumer_lock); return ptr; } static inline void ptr_ring_consume_irq(struct ptr_ring r) { void ptr; spin_lock_irq(&r->consumer_lock); ptr = __ptr_ring_consume(r); spin_unlock_irq(&r->consumer_lock); return ptr; } static inline void ptr_ring_consume_any(struct ptr_ring r) { unsigned long flags; void ptr; spin_lock_irqsave(&r->consumer_lock, flags); ptr = __ptr_ring_consume(r); spin_unlock_irqrestore(&r->consumer_lock, flags); return ptr; } static inline void ptr_ring_consume_bh(struct ptr_ring r) { void ptr; spin_lock_bh(&r->consumer_lock); ptr = __ptr_ring_consume(r); spin_unlock_bh(&r->consumer_lock); return ptr; } static inline int ptr_ring_consume_batched(struct ptr_ring r, void *array, int n) { int ret; spin_lock(&r->consumer_lock); ret = __ptr_ring_consume_batched(r, array, n); spin_unlock(&r->consumer_lock); return ret; } static inline int ptr_ring_consume_batched_irq(struct ptr_ring r, void *array, int n) { int ret; spin_lock_irq(&r->consumer_lock); ret = __ptr_ring_consume_batched(r, array, n); spin_unlock_irq(&r->consumer_lock); return ret; } static inline int ptr_ring_consume_batched_any(struct ptr_ring r, void *array, int n) { unsigned long flags; int ret; spin_lock_irqsave(&r->consumer_lock, flags); ret = __ptr_ring_consume_batched(r, array, n); spin_unlock_irqrestore(&r->consumer_lock, flags); return ret; } static inline int ptr_ring_consume_batched_bh(struct ptr_ring r, void *array, int n) { int ret; spin_lock_bh(&r->consumer_lock); ret = __ptr_ring_consume_batched(r, array, n); spin_unlock_bh(&r->consumer_lock); return ret; } / Cast to structure type and call a function without discarding from FIFO. * Function must return a value. * Callers must take consumer_lock. / #define __PTR_RING_PEEK_CALL(r, f) ((f)(__ptr_ring_peek(r))) #define PTR_RING_PEEK_CALL(r, f) ({ \ typeof((f)(NULL)) __PTR_RING_PEEK_CALL_v; \ \ spin_lock(&(r)->consumer_lock); \ __PTR_RING_PEEK_CALL_v = __PTR_RING_PEEK_CALL(r, f); \ spin_unlock(&(r)->consumer_lock); \ __PTR_RING_PEEK_CALL_v; \ }) #define PTR_RING_PEEK_CALL_IRQ(r, f) ({ \ typeof((f)(NULL)) __PTR_RING_PEEK_CALL_v; \ \ spin_lock_irq(&(r)->consumer_lock); \ __PTR_RING_PEEK_CALL_v = __PTR_RING_PEEK_CALL(r, f); \ spin_unlock_irq(&(r)->consumer_lock); \ __PTR_RING_PEEK_CALL_v; \ }) #define PTR_RING_PEEK_CALL_BH(r, f) ({ \ typeof((f)(NULL)) __PTR_RING_PEEK_CALL_v; \ \ spin_lock_bh(&(r)->consumer_lock); \ __PTR_RING_PEEK_CALL_v = __PTR_RING_PEEK_CALL(r, f); \ spin_unlock_bh(&(r)->consumer_lock); \ __PTR_RING_PEEK_CALL_v; \ }) #define PTR_RING_PEEK_CALL_ANY(r, f) ({ \ typeof((f)(NULL)) __PTR_RING_PEEK_CALL_v; \ unsigned long __PTR_RING_PEEK_CALL_f;\ \ spin_lock_irqsave(&(r)->consumer_lock, __PTR_RING_PEEK_CALL_f); \ __PTR_RING_PEEK_CALL_v = __PTR_RING_PEEK_CALL(r, f); \ spin_unlock_irqrestore(&(r)->consumer_lock, __PTR_RING_PEEK_CALL_f); \ __PTR_RING_PEEK_CALL_v; \ }) / Not all gfp_t flags (besides GFP_KERNEL) are allowed. See * documentation for vmalloc for which of them are legal. / static inline void __ptr_ring_init_queue_alloc(unsigned int size, gfp_t gfp) { if (size > KMALLOC_MAX_SIZE / sizeof(void )) return NULL; return kvmalloc_array(size, sizeof(void ), gfp \| __GFP_ZERO); } static inline void __ptr_ring_set_size(struct ptr_ring r, int size) { r->size = size; r->batch = SMP_CACHE_BYTES * 2 / sizeof((r->queue)); / We need to set batch at least to 1 to make logic * in __ptr_ring_discard_one work correctly. * Batching too much (because ring is small) would cause a lot of * burstiness. Needs tuning, for now disable batching. / if (r->batch > r->size / 2 \|\| !r->batch) r->batch = 1; } static inline int ptr_ring_init(struct ptr_ring r, int size, gfp_t gfp) { r->queue = __ptr_ring_init_queue_alloc(size, gfp); if (!r->queue) return -ENOMEM; __ptr_ring_set_size(r, size); r->producer = r->consumer_head = r->consumer_tail = 0; spin_lock_init(&r->producer_lock); spin_lock_init(&r->consumer_lock); return 0; } /* * Return entries into ring. Destroy entries that don't fit. * * Note: this is expected to be a rare slow path operation. * * Note: producer lock is nested within consumer lock, so if you * resize you must make sure all uses nest correctly. * In particular if you consume ring in interrupt or BH context, you must * disable interrupts/BH when doing so. / static inline void ptr_ring_unconsume(struct ptr_ring r, void *batch, int n, void (destroy)(void )) { unsigned long flags; int head; spin_lock_irqsave(&r->consumer_lock, flags); spin_lock(&r->producer_lock); if (!r->size) goto done; / * Clean out buffered entries (for simplicity). This way following code * can test entries for NULL and if not assume they are valid. / head = r->consumer_head - 1; while (likely(head >= r->consumer_tail)) r->queue[head--] = NULL; r->consumer_tail = r->consumer_head; / * Go over entries in batch, start moving head back and copy entries. * Stop when we run into previously unconsumed entries. / while (n) { head = r->consumer_head - 1; if (head < 0) head = r->size - 1; if (r->queue[head]) { / This batch entry will have to be destroyed. / goto done; } r->queue[head] = batch[--n]; r->consumer_tail = head; / matching READ_ONCE in __ptr_ring_empty for lockless tests / WRITE_ONCE(r->consumer_head, head); } done: / Destroy all entries left in the batch. / while (n) destroy(batch[--n]); spin_unlock(&r->producer_lock); spin_unlock_irqrestore(&r->consumer_lock, flags); } static inline void __ptr_ring_swap_queue(struct ptr_ring r, void *queue, int size, gfp_t gfp, void (destroy)(void )) { int producer = 0; void old; void ptr; while ((ptr = __ptr_ring_consume(r))) if (producer < size) queue[producer++] = ptr; else if (destroy) destroy(ptr); if (producer >= size) producer = 0; __ptr_ring_set_size(r, size); r->producer = producer; r->consumer_head = 0; r->consumer_tail = 0; old = r->queue; r->queue = queue; return old; } /* * Note: producer lock is nested within consumer lock, so if you * resize you must make sure all uses nest correctly. * In particular if you consume ring in interrupt or BH context, you must * disable interrupts/BH when doing so. / static inline int ptr_ring_resize(struct ptr_ring r, int size, gfp_t gfp, void (destroy)(void )) { unsigned long flags; void queue = __ptr_ring_init_queue_alloc(size, gfp); void old; if (!queue) return -ENOMEM; spin_lock_irqsave(&(r)->consumer_lock, flags); spin_lock(&(r)->producer_lock); old = __ptr_ring_swap_queue(r, queue, size, gfp, destroy); spin_unlock(&(r)->producer_lock); spin_unlock_irqrestore(&(r)->consumer_lock, flags); kvfree(old); return 0; } /* * Note: producer lock is nested within consumer lock, so if you * resize you must make sure all uses nest correctly. * In particular if you consume ring in interrupt or BH context, you must * disable interrupts/BH when doing so. / static inline int ptr_ring_resize_multiple(struct ptr_ring rings, unsigned int nrings, int size, gfp_t gfp, void (destroy)(void )) { unsigned long flags; void *queues; int i; queues = kmalloc_array(nrings, sizeof(queues), gfp); if (!queues) goto noqueues; for (i = 0; i < nrings; ++i) { queues[i] = __ptr_ring_init_queue_alloc(size, gfp); if (!queues[i]) goto nomem; } for (i = 0; i < nrings; ++i) { spin_lock_irqsave(&(rings[i])->consumer_lock, flags); spin_lock(&(rings[i])->producer_lock); queues[i] = __ptr_ring_swap_queue(rings[i], queues[i], size, gfp, destroy); spin_unlock(&(rings[i])->producer_lock); spin_unlock_irqrestore(&(rings[i])->consumer_lock, flags); } for (i = 0; i < nrings; ++i) kvfree(queues[i]); kfree(queues); return 0; nomem: while (--i >= 0) kvfree(queues[i]); kfree(queues); noqueues: return -ENOMEM; } static inline void ptr_ring_cleanup(struct ptr_ring r, void (destroy)(void )) { void ptr; if (destroy) while ((ptr = ptr_ring_consume(r))) destroy(ptr); kvfree(r->queue); } #endif /* _LINUX_PTR_RING_H */

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