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_pr.h>
30
31 #include "ck_internal.h"
32
33 /*
34 * This is a tournament barrier implementation. Threads are statically
35 * assigned roles to perform for each round of the barrier. Winners
36 * move on to the next round, while losers spin in their current rounds
37 * on their own flags. During the last round, the champion of the tournament
38 * sets the last flag that begins the wakeup process.
39 */
40
41 enum {
42 CK_BARRIER_TOURNAMENT_BYE,
43 CK_BARRIER_TOURNAMENT_CHAMPION,
44 CK_BARRIER_TOURNAMENT_DROPOUT,
45 CK_BARRIER_TOURNAMENT_LOSER,
46 CK_BARRIER_TOURNAMENT_WINNER
47 };
48
49 void
ck_barrier_tournament_subscribe(struct ck_barrier_tournament * barrier,struct ck_barrier_tournament_state * state)50 ck_barrier_tournament_subscribe(struct ck_barrier_tournament *barrier,
51 struct ck_barrier_tournament_state *state)
52 {
53
54 state->sense = ~0;
55 state->vpid = ck_pr_faa_uint(&barrier->tid, 1);
56 return;
57 }
58
59 void
ck_barrier_tournament_init(struct ck_barrier_tournament * barrier,struct ck_barrier_tournament_round ** rounds,unsigned int nthr)60 ck_barrier_tournament_init(struct ck_barrier_tournament *barrier,
61 struct ck_barrier_tournament_round **rounds,
62 unsigned int nthr)
63 {
64 unsigned int i, k, size, twok, twokm1, imod2k;
65
66 ck_pr_store_uint(&barrier->tid, 0);
67 barrier->size = size = ck_barrier_tournament_size(nthr);
68
69 for (i = 0; i < nthr; ++i) {
70 /* The first role is always CK_BARRIER_TOURNAMENT_DROPOUT. */
71 rounds[i][0].flag = 0;
72 rounds[i][0].role = CK_BARRIER_TOURNAMENT_DROPOUT;
73 for (k = 1, twok = 2, twokm1 = 1; k < size; ++k, twokm1 = twok, twok <<= 1) {
74 rounds[i][k].flag = 0;
75
76 imod2k = i & (twok - 1);
77 if (imod2k == 0) {
78 if ((i + twokm1 < nthr) && (twok < nthr))
79 rounds[i][k].role = CK_BARRIER_TOURNAMENT_WINNER;
80 else if (i + twokm1 >= nthr)
81 rounds[i][k].role = CK_BARRIER_TOURNAMENT_BYE;
82 }
83
84 if (imod2k == twokm1)
85 rounds[i][k].role = CK_BARRIER_TOURNAMENT_LOSER;
86 else if ((i == 0) && (twok >= nthr))
87 rounds[i][k].role = CK_BARRIER_TOURNAMENT_CHAMPION;
88
89 if (rounds[i][k].role == CK_BARRIER_TOURNAMENT_LOSER)
90 rounds[i][k].opponent = &rounds[i - twokm1][k].flag;
91 else if (rounds[i][k].role == CK_BARRIER_TOURNAMENT_WINNER ||
92 rounds[i][k].role == CK_BARRIER_TOURNAMENT_CHAMPION)
93 rounds[i][k].opponent = &rounds[i + twokm1][k].flag;
94 }
95 }
96
97 ck_pr_store_ptr(&barrier->rounds, rounds);
98 return;
99 }
100
101 unsigned int
ck_barrier_tournament_size(unsigned int nthr)102 ck_barrier_tournament_size(unsigned int nthr)
103 {
104
105 return (ck_internal_log(ck_internal_power_2(nthr)) + 1);
106 }
107
108 void
ck_barrier_tournament(struct ck_barrier_tournament * barrier,struct ck_barrier_tournament_state * state)109 ck_barrier_tournament(struct ck_barrier_tournament *barrier,
110 struct ck_barrier_tournament_state *state)
111 {
112 struct ck_barrier_tournament_round **rounds = ck_pr_load_ptr(&barrier->rounds);
113 int round = 1;
114
115 if (barrier->size == 1)
116 return;
117
118 for (;; ++round) {
119 switch (rounds[state->vpid][round].role) {
120 case CK_BARRIER_TOURNAMENT_BYE:
121 break;
122 case CK_BARRIER_TOURNAMENT_CHAMPION:
123 /*
124 * The CK_BARRIER_TOURNAMENT_CHAMPION waits until it wins the tournament; it then
125 * sets the final flag before the wakeup phase of the barrier.
126 */
127 while (ck_pr_load_uint(&rounds[state->vpid][round].flag) != state->sense)
128 ck_pr_stall();
129
130 ck_pr_store_uint(rounds[state->vpid][round].opponent, state->sense);
131 goto wakeup;
132 case CK_BARRIER_TOURNAMENT_DROPOUT:
133 /* NOTREACHED */
134 break;
135 case CK_BARRIER_TOURNAMENT_LOSER:
136 /*
137 * CK_BARRIER_TOURNAMENT_LOSERs set the flags of their opponents and wait until
138 * their opponents release them after the tournament is over.
139 */
140 ck_pr_store_uint(rounds[state->vpid][round].opponent, state->sense);
141 while (ck_pr_load_uint(&rounds[state->vpid][round].flag) != state->sense)
142 ck_pr_stall();
143
144 goto wakeup;
145 case CK_BARRIER_TOURNAMENT_WINNER:
146 /*
147 * CK_BARRIER_TOURNAMENT_WINNERs wait until their current opponent sets their flag; they then
148 * continue to the next round of the tournament.
149 */
150 while (ck_pr_load_uint(&rounds[state->vpid][round].flag) != state->sense)
151 ck_pr_stall();
152 break;
153 }
154 }
155
156 wakeup:
157 for (round -= 1 ;; --round) {
158 switch (rounds[state->vpid][round].role) {
159 case CK_BARRIER_TOURNAMENT_BYE:
160 break;
161 case CK_BARRIER_TOURNAMENT_CHAMPION:
162 /* NOTREACHED */
163 break;
164 case CK_BARRIER_TOURNAMENT_DROPOUT:
165 goto leave;
166 break;
167 case CK_BARRIER_TOURNAMENT_LOSER:
168 /* NOTREACHED */
169 break;
170 case CK_BARRIER_TOURNAMENT_WINNER:
171 /*
172 * Winners inform their old opponents the tournament is over
173 * by setting their flags.
174 */
175 ck_pr_store_uint(rounds[state->vpid][round].opponent, state->sense);
176 break;
177 }
178 }
179
180 leave:
181 ck_pr_fence_memory();
182 state->sense = ~state->sense;
183 return;
184 }
185