2014-12-31 23:19:16 +00:00
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/*-
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* Copyright (c) 2014 Chelsio Communications, Inc.
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* All rights reserved.
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* Written by: Navdeep Parhar <np@FreeBSD.org>
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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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#include <sys/cdefs.h>
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__FBSDID("$FreeBSD$");
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#include <sys/types.h>
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#include <sys/param.h>
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#include <sys/systm.h>
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#include <sys/counter.h>
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#include <sys/lock.h>
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#include <sys/malloc.h>
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#include <machine/cpu.h>
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#include "t4_mp_ring.h"
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2015-01-16 01:32:40 +00:00
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#if defined(__i386__)
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#define atomic_cmpset_acq_64 atomic_cmpset_64
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#define atomic_cmpset_rel_64 atomic_cmpset_64
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#endif
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2014-12-31 23:19:16 +00:00
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union ring_state {
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struct {
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uint16_t pidx_head;
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uint16_t pidx_tail;
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uint16_t cidx;
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uint16_t flags;
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};
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uint64_t state;
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};
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enum {
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IDLE = 0, /* consumer ran to completion, nothing more to do. */
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BUSY, /* consumer is running already, or will be shortly. */
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STALLED, /* consumer stopped due to lack of resources. */
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ABDICATED, /* consumer stopped even though there was work to be
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done because it wants another thread to take over. */
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};
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static inline uint16_t
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space_available(struct mp_ring *r, union ring_state s)
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{
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uint16_t x = r->size - 1;
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if (s.cidx == s.pidx_head)
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return (x);
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else if (s.cidx > s.pidx_head)
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return (s.cidx - s.pidx_head - 1);
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else
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return (x - s.pidx_head + s.cidx);
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}
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static inline uint16_t
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increment_idx(struct mp_ring *r, uint16_t idx, uint16_t n)
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{
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int x = r->size - idx;
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MPASS(x > 0);
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return (x > n ? idx + n : n - x);
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}
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/* Consumer is about to update the ring's state to s */
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static inline uint16_t
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state_to_flags(union ring_state s, int abdicate)
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{
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if (s.cidx == s.pidx_tail)
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return (IDLE);
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else if (abdicate && s.pidx_tail != s.pidx_head)
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return (ABDICATED);
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return (BUSY);
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}
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/*
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* Caller passes in a state, with a guarantee that there is work to do and that
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* all items up to the pidx_tail in the state are visible.
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*/
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static void
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drain_ring(struct mp_ring *r, union ring_state os, uint16_t prev, int budget)
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{
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union ring_state ns;
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int n, pending, total;
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uint16_t cidx = os.cidx;
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uint16_t pidx = os.pidx_tail;
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MPASS(os.flags == BUSY);
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MPASS(cidx != pidx);
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if (prev == IDLE)
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counter_u64_add(r->starts, 1);
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pending = 0;
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total = 0;
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while (cidx != pidx) {
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/* Items from cidx to pidx are available for consumption. */
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n = r->drain(r, cidx, pidx);
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if (n == 0) {
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critical_enter();
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do {
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os.state = ns.state = r->state;
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ns.cidx = cidx;
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ns.flags = STALLED;
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} while (atomic_cmpset_64(&r->state, os.state,
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ns.state) == 0);
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critical_exit();
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if (prev != STALLED)
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counter_u64_add(r->stalls, 1);
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else if (total > 0) {
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counter_u64_add(r->restarts, 1);
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counter_u64_add(r->stalls, 1);
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}
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break;
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}
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cidx = increment_idx(r, cidx, n);
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pending += n;
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total += n;
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/*
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* We update the cidx only if we've caught up with the pidx, the
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* real cidx is getting too far ahead of the one visible to
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* everyone else, or we have exceeded our budget.
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*/
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if (cidx != pidx && pending < 64 && total < budget)
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continue;
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critical_enter();
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do {
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os.state = ns.state = r->state;
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ns.cidx = cidx;
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ns.flags = state_to_flags(ns, total >= budget);
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} while (atomic_cmpset_acq_64(&r->state, os.state, ns.state) == 0);
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critical_exit();
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if (ns.flags == ABDICATED)
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counter_u64_add(r->abdications, 1);
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if (ns.flags != BUSY) {
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/* Wrong loop exit if we're going to stall. */
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MPASS(ns.flags != STALLED);
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if (prev == STALLED) {
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MPASS(total > 0);
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counter_u64_add(r->restarts, 1);
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}
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break;
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}
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/*
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* The acquire style atomic above guarantees visibility of items
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* associated with any pidx change that we notice here.
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*/
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pidx = ns.pidx_tail;
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pending = 0;
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}
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}
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int
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mp_ring_alloc(struct mp_ring **pr, int size, void *cookie, ring_drain_t drain,
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ring_can_drain_t can_drain, struct malloc_type *mt, int flags)
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{
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struct mp_ring *r;
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/* All idx are 16b so size can be 65536 at most */
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if (pr == NULL || size < 2 || size > 65536 || drain == NULL ||
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can_drain == NULL)
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return (EINVAL);
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*pr = NULL;
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flags &= M_NOWAIT | M_WAITOK;
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MPASS(flags != 0);
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r = malloc(__offsetof(struct mp_ring, items[size]), mt, flags | M_ZERO);
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if (r == NULL)
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return (ENOMEM);
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r->size = size;
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r->cookie = cookie;
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r->mt = mt;
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r->drain = drain;
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r->can_drain = can_drain;
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r->enqueues = counter_u64_alloc(flags);
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r->drops = counter_u64_alloc(flags);
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r->starts = counter_u64_alloc(flags);
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r->stalls = counter_u64_alloc(flags);
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r->restarts = counter_u64_alloc(flags);
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r->abdications = counter_u64_alloc(flags);
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if (r->enqueues == NULL || r->drops == NULL || r->starts == NULL ||
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r->stalls == NULL || r->restarts == NULL ||
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r->abdications == NULL) {
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mp_ring_free(r);
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return (ENOMEM);
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}
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*pr = r;
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return (0);
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}
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void
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mp_ring_free(struct mp_ring *r)
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{
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if (r == NULL)
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return;
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if (r->enqueues != NULL)
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counter_u64_free(r->enqueues);
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if (r->drops != NULL)
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counter_u64_free(r->drops);
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if (r->starts != NULL)
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counter_u64_free(r->starts);
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if (r->stalls != NULL)
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counter_u64_free(r->stalls);
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if (r->restarts != NULL)
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counter_u64_free(r->restarts);
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if (r->abdications != NULL)
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counter_u64_free(r->abdications);
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free(r, r->mt);
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}
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/*
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* Enqueue n items and maybe drain the ring for some time.
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*
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* Returns an errno.
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*/
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int
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mp_ring_enqueue(struct mp_ring *r, void **items, int n, int budget)
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{
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union ring_state os, ns;
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uint16_t pidx_start, pidx_stop;
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int i;
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MPASS(items != NULL);
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MPASS(n > 0);
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/*
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* Reserve room for the new items. Our reservation, if successful, is
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* from 'pidx_start' to 'pidx_stop'.
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*/
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for (;;) {
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os.state = r->state;
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if (n >= space_available(r, os)) {
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counter_u64_add(r->drops, n);
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MPASS(os.flags != IDLE);
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if (os.flags == STALLED)
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mp_ring_check_drainage(r, 0);
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return (ENOBUFS);
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}
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ns.state = os.state;
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ns.pidx_head = increment_idx(r, os.pidx_head, n);
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critical_enter();
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if (atomic_cmpset_64(&r->state, os.state, ns.state))
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break;
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critical_exit();
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cpu_spinwait();
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}
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pidx_start = os.pidx_head;
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pidx_stop = ns.pidx_head;
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/*
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* Wait for other producers who got in ahead of us to enqueue their
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* items, one producer at a time. It is our turn when the ring's
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* pidx_tail reaches the begining of our reservation (pidx_start).
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*/
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while (ns.pidx_tail != pidx_start) {
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cpu_spinwait();
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ns.state = r->state;
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}
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/* Now it is our turn to fill up the area we reserved earlier. */
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i = pidx_start;
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do {
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r->items[i] = *items++;
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if (__predict_false(++i == r->size))
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i = 0;
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} while (i != pidx_stop);
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/*
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* Update the ring's pidx_tail. The release style atomic guarantees
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* that the items are visible to any thread that sees the updated pidx.
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*/
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do {
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os.state = ns.state = r->state;
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ns.pidx_tail = pidx_stop;
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ns.flags = BUSY;
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} while (atomic_cmpset_rel_64(&r->state, os.state, ns.state) == 0);
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critical_exit();
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counter_u64_add(r->enqueues, n);
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/*
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* Turn into a consumer if some other thread isn't active as a consumer
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* already.
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*/
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if (os.flags != BUSY)
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drain_ring(r, ns, os.flags, budget);
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return (0);
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}
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void
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mp_ring_check_drainage(struct mp_ring *r, int budget)
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{
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union ring_state os, ns;
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os.state = r->state;
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if (os.flags != STALLED || os.pidx_head != os.pidx_tail ||
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r->can_drain(r) == 0)
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return;
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MPASS(os.cidx != os.pidx_tail); /* implied by STALLED */
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ns.state = os.state;
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ns.flags = BUSY;
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/*
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* The acquire style atomic guarantees visibility of items associated
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* with the pidx that we read here.
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*/
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if (!atomic_cmpset_acq_64(&r->state, os.state, ns.state))
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return;
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drain_ring(r, ns, os.flags, budget);
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}
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void
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mp_ring_reset_stats(struct mp_ring *r)
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{
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counter_u64_zero(r->enqueues);
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counter_u64_zero(r->drops);
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counter_u64_zero(r->starts);
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counter_u64_zero(r->stalls);
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counter_u64_zero(r->restarts);
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counter_u64_zero(r->abdications);
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}
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int
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mp_ring_is_idle(struct mp_ring *r)
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{
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union ring_state s;
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s.state = r->state;
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if (s.pidx_head == s.pidx_tail && s.pidx_tail == s.cidx &&
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s.flags == IDLE)
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return (1);
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return (0);
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}
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