/*-
* SPDX-License-Identifier: BSD-2-Clause-FreeBSD
*
* Copyright (c) 2007-2009 Kip Macy <kmacy@freebsd.org>
* 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 <machine/cpu.h>
#ifdef DEBUG_BUFRING
#include <sys/lock.h>
#include <sys/mutex.h>
#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]; <see <1>>
* 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);
* <condition is false and code uses invalid(old) buf>`
*
* <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
