/*- * SPDX-License-Identifier: BSD-2-Clause-FreeBSD * * Copyright (c) 2007-2009 Kip Macy * All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. * * $FreeBSD$ * */ #ifndef _SYS_BUF_RING_H_ #define _SYS_BUF_RING_H_ #include #ifdef DEBUG_BUFRING #include #include #endif struct buf_ring { volatile uint32_t br_prod_head; volatile uint32_t br_prod_tail; int br_prod_size; int br_prod_mask; uint64_t br_drops; volatile uint32_t br_cons_head __aligned(CACHE_LINE_SIZE); volatile uint32_t br_cons_tail; int br_cons_size; int br_cons_mask; #ifdef DEBUG_BUFRING struct mtx *br_lock; #endif void *br_ring[0] __aligned(CACHE_LINE_SIZE); }; /* * multi-producer safe lock-free ring buffer enqueue * */ static __inline int buf_ring_enqueue(struct buf_ring *br, void *buf) { uint32_t prod_head, prod_next, cons_tail; #ifdef DEBUG_BUFRING int i; /* * Note: It is possible to encounter an mbuf that was removed * via drbr_peek(), and then re-added via drbr_putback() and * trigger a spurious panic. */ for (i = br->br_cons_head; i != br->br_prod_head; i = ((i + 1) & br->br_cons_mask)) if (br->br_ring[i] == buf) panic("buf=%p already enqueue at %d prod=%d cons=%d", buf, i, br->br_prod_tail, br->br_cons_tail); #endif critical_enter(); do { prod_head = br->br_prod_head; prod_next = (prod_head + 1) & br->br_prod_mask; cons_tail = br->br_cons_tail; if (prod_next == cons_tail) { rmb(); if (prod_head == br->br_prod_head && cons_tail == br->br_cons_tail) { br->br_drops++; critical_exit(); return (ENOBUFS); } continue; } } while (!atomic_cmpset_acq_int(&br->br_prod_head, prod_head, prod_next)); #ifdef DEBUG_BUFRING if (br->br_ring[prod_head] != NULL) panic("dangling value in enqueue"); #endif br->br_ring[prod_head] = buf; /* * If there are other enqueues in progress * that preceded us, we need to wait for them * to complete */ while (br->br_prod_tail != prod_head) cpu_spinwait(); atomic_store_rel_int(&br->br_prod_tail, prod_next); critical_exit(); return (0); } /* * multi-consumer safe dequeue * */ static __inline void * buf_ring_dequeue_mc(struct buf_ring *br) { uint32_t cons_head, cons_next; void *buf; critical_enter(); do { cons_head = br->br_cons_head; cons_next = (cons_head + 1) & br->br_cons_mask; if (cons_head == br->br_prod_tail) { critical_exit(); return (NULL); } } while (!atomic_cmpset_acq_int(&br->br_cons_head, cons_head, cons_next)); buf = br->br_ring[cons_head]; #ifdef DEBUG_BUFRING br->br_ring[cons_head] = NULL; #endif /* * If there are other dequeues in progress * that preceded us, we need to wait for them * to complete */ while (br->br_cons_tail != cons_head) cpu_spinwait(); atomic_store_rel_int(&br->br_cons_tail, cons_next); critical_exit(); return (buf); } /* * single-consumer dequeue * use where dequeue is protected by a lock * e.g. a network driver's tx queue lock */ static __inline void * buf_ring_dequeue_sc(struct buf_ring *br) { uint32_t cons_head, cons_next; #ifdef PREFETCH_DEFINED uint32_t cons_next_next; #endif uint32_t prod_tail; void *buf; /* * This is a workaround to allow using buf_ring on ARM and ARM64. * ARM64TODO: Fix buf_ring in a generic way. * REMARKS: It is suspected that br_cons_head does not require * load_acq operation, but this change was extensively tested * and confirmed it's working. To be reviewed once again in * FreeBSD-12. * * Preventing following situation: * Core(0) - buf_ring_enqueue() Core(1) - buf_ring_dequeue_sc() * ----------------------------------------- ---------------------------------------------- * * cons_head = br->br_cons_head; * atomic_cmpset_acq_32(&br->br_prod_head, ...)); * buf = br->br_ring[cons_head]; > * br->br_ring[prod_head] = buf; * atomic_store_rel_32(&br->br_prod_tail, ...); * prod_tail = br->br_prod_tail; * if (cons_head == prod_tail) * return (NULL); * ` * * <1> Load (on core 1) from br->br_ring[cons_head] can be reordered (speculative readed) by CPU. */ #if defined(__arm__) || defined(__aarch64__) cons_head = atomic_load_acq_32(&br->br_cons_head); #else cons_head = br->br_cons_head; #endif prod_tail = atomic_load_acq_32(&br->br_prod_tail); cons_next = (cons_head + 1) & br->br_cons_mask; #ifdef PREFETCH_DEFINED cons_next_next = (cons_head + 2) & br->br_cons_mask; #endif if (cons_head == prod_tail) return (NULL); #ifdef PREFETCH_DEFINED if (cons_next != prod_tail) { prefetch(br->br_ring[cons_next]); if (cons_next_next != prod_tail) prefetch(br->br_ring[cons_next_next]); } #endif br->br_cons_head = cons_next; buf = br->br_ring[cons_head]; #ifdef DEBUG_BUFRING br->br_ring[cons_head] = NULL; if (!mtx_owned(br->br_lock)) panic("lock not held on single consumer dequeue"); if (br->br_cons_tail != cons_head) panic("inconsistent list cons_tail=%d cons_head=%d", br->br_cons_tail, cons_head); #endif br->br_cons_tail = cons_next; return (buf); } /* * single-consumer advance after a peek * use where it is protected by a lock * e.g. a network driver's tx queue lock */ static __inline void buf_ring_advance_sc(struct buf_ring *br) { uint32_t cons_head, cons_next; uint32_t prod_tail; cons_head = br->br_cons_head; prod_tail = br->br_prod_tail; cons_next = (cons_head + 1) & br->br_cons_mask; if (cons_head == prod_tail) return; br->br_cons_head = cons_next; #ifdef DEBUG_BUFRING br->br_ring[cons_head] = NULL; #endif br->br_cons_tail = cons_next; } /* * Used to return a buffer (most likely already there) * to the top of the ring. The caller should *not* * have used any dequeue to pull it out of the ring * but instead should have used the peek() function. * This is normally used where the transmit queue * of a driver is full, and an mbuf must be returned. * Most likely whats in the ring-buffer is what * is being put back (since it was not removed), but * sometimes the lower transmit function may have * done a pullup or other function that will have * changed it. As an optimization we always put it * back (since jhb says the store is probably cheaper), * if we have to do a multi-queue version we will need * the compare and an atomic. */ static __inline void buf_ring_putback_sc(struct buf_ring *br, void *new) { KASSERT(br->br_cons_head != br->br_prod_tail, ("Buf-Ring has none in putback")) ; br->br_ring[br->br_cons_head] = new; } /* * return a pointer to the first entry in the ring * without modifying it, or NULL if the ring is empty * race-prone if not protected by a lock */ static __inline void * buf_ring_peek(struct buf_ring *br) { #ifdef DEBUG_BUFRING if ((br->br_lock != NULL) && !mtx_owned(br->br_lock)) panic("lock not held on single consumer dequeue"); #endif /* * I believe it is safe to not have a memory barrier * here because we control cons and tail is worst case * a lagging indicator so we worst case we might * return NULL immediately after a buffer has been enqueued */ if (br->br_cons_head == br->br_prod_tail) return (NULL); return (br->br_ring[br->br_cons_head]); } static __inline void * buf_ring_peek_clear_sc(struct buf_ring *br) { #ifdef DEBUG_BUFRING void *ret; if (!mtx_owned(br->br_lock)) panic("lock not held on single consumer dequeue"); #endif if (br->br_cons_head == br->br_prod_tail) return (NULL); #if defined(__arm__) || defined(__aarch64__) /* * The barrier is required there on ARM and ARM64 to ensure, that * br->br_ring[br->br_cons_head] will not be fetched before the above * condition is checked. * Without the barrier, it is possible, that buffer will be fetched * before the enqueue will put mbuf into br, then, in the meantime, the * enqueue will update the array and the br_prod_tail, and the * conditional check will be true, so we will return previously fetched * (and invalid) buffer. */ atomic_thread_fence_acq(); #endif #ifdef DEBUG_BUFRING /* * Single consumer, i.e. cons_head will not move while we are * running, so atomic_swap_ptr() is not necessary here. */ ret = br->br_ring[br->br_cons_head]; br->br_ring[br->br_cons_head] = NULL; return (ret); #else return (br->br_ring[br->br_cons_head]); #endif } static __inline int buf_ring_full(struct buf_ring *br) { return (((br->br_prod_head + 1) & br->br_prod_mask) == br->br_cons_tail); } static __inline int buf_ring_empty(struct buf_ring *br) { return (br->br_cons_head == br->br_prod_tail); } static __inline int buf_ring_count(struct buf_ring *br) { return ((br->br_prod_size + br->br_prod_tail - br->br_cons_tail) & br->br_prod_mask); } struct buf_ring *buf_ring_alloc(int count, struct malloc_type *type, int flags, struct mtx *); void buf_ring_free(struct buf_ring *br, struct malloc_type *type); #endif