1 /*
2 * Copyright 2011-2015 Samy Al Bahra.
3 * Copyright 2011 David Joseph.
4 * All rights reserved.
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
8 * are met:
9 * 1. Redistributions of source code must retain the above copyright
10 * notice, this list of conditions and the following disclaimer.
11 * 2. Redistributions in binary form must reproduce the above copyright
12 * notice, this list of conditions and the following disclaimer in the
13 * documentation and/or other materials provided with the distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
16 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
17 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
18 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
19 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
20 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
21 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
22 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
23 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
24 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
25 * SUCH DAMAGE.
26 */
27
28 #include <ck_barrier.h>
29 #include <ck_cc.h>
30 #include <ck_pr.h>
31 #include <ck_spinlock.h>
32
33 #include "ck_internal.h"
34
35 void
ck_barrier_dissemination_init(struct ck_barrier_dissemination * barrier,struct ck_barrier_dissemination_flag ** barrier_internal,unsigned int nthr)36 ck_barrier_dissemination_init(struct ck_barrier_dissemination *barrier,
37 struct ck_barrier_dissemination_flag **barrier_internal,
38 unsigned int nthr)
39 {
40 unsigned int i, j, k, size, offset;
41 bool p = nthr & (nthr - 1);
42
43 barrier->nthr = nthr;
44 barrier->size = size = ck_internal_log(ck_internal_power_2(nthr));
45 ck_pr_store_uint(&barrier->tid, 0);
46
47 for (i = 0; i < nthr; ++i) {
48 barrier[i].flags[0] = barrier_internal[i];
49 barrier[i].flags[1] = barrier_internal[i] + size;
50 }
51
52 for (i = 0; i < nthr; ++i) {
53 for (k = 0, offset = 1; k < size; ++k, offset <<= 1) {
54 /*
55 * Determine the thread's partner, j, for the current round, k.
56 * Partners are chosen such that by the completion of the barrier,
57 * every thread has been directly (having one of its flag set) or
58 * indirectly (having one of its partners's flags set) signaled
59 * by every other thread in the barrier.
60 */
61 if (p == false)
62 j = (i + offset) & (nthr - 1);
63 else
64 j = (i + offset) % nthr;
65
66 /* Set the thread's partner for round k. */
67 barrier[i].flags[0][k].pflag = &barrier[j].flags[0][k].tflag;
68 barrier[i].flags[1][k].pflag = &barrier[j].flags[1][k].tflag;
69
70 /* Set the thread's flags to false. */
71 barrier[i].flags[0][k].tflag = barrier[i].flags[1][k].tflag = 0;
72 }
73 }
74
75 return;
76 }
77
78 void
ck_barrier_dissemination_subscribe(struct ck_barrier_dissemination * barrier,struct ck_barrier_dissemination_state * state)79 ck_barrier_dissemination_subscribe(struct ck_barrier_dissemination *barrier,
80 struct ck_barrier_dissemination_state *state)
81 {
82
83 state->parity = 0;
84 state->sense = ~0;
85 state->tid = ck_pr_faa_uint(&barrier->tid, 1);
86 return;
87 }
88
89 unsigned int
ck_barrier_dissemination_size(unsigned int nthr)90 ck_barrier_dissemination_size(unsigned int nthr)
91 {
92
93 return (ck_internal_log(ck_internal_power_2(nthr)) << 1);
94 }
95
96 void
ck_barrier_dissemination(struct ck_barrier_dissemination * barrier,struct ck_barrier_dissemination_state * state)97 ck_barrier_dissemination(struct ck_barrier_dissemination *barrier,
98 struct ck_barrier_dissemination_state *state)
99 {
100 unsigned int i;
101 unsigned int size = barrier->size;
102
103 for (i = 0; i < size; ++i) {
104 unsigned int *pflag, *tflag;
105
106 pflag = barrier[state->tid].flags[state->parity][i].pflag;
107 tflag = &barrier[state->tid].flags[state->parity][i].tflag;
108
109 /* Unblock current partner. */
110 ck_pr_store_uint(pflag, state->sense);
111
112 /* Wait until some other thread unblocks this one. */
113 while (ck_pr_load_uint(tflag) != state->sense)
114 ck_pr_stall();
115 }
116
117 /*
118 * Dissemination barriers use two sets of flags to prevent race conditions
119 * between successive calls to the barrier. Parity indicates which set will
120 * be used for the next barrier. They also use a sense reversal technique
121 * to avoid re-initialization of the flags for every two calls to the barrier.
122 */
123 if (state->parity == 1)
124 state->sense = ~state->sense;
125
126 state->parity = 1 - state->parity;
127
128 ck_pr_fence_acquire();
129 return;
130 }
131