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