1 /* $NetBSD: t_dekker.c,v 1.3 2022/04/10 11:36:32 riastradh Exp $ */ 2 3 /*- 4 * Copyright (c) 2022 The NetBSD Foundation, Inc. 5 * All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 16 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 17 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 18 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 19 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 20 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 21 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 22 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 23 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 24 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 25 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 26 * POSSIBILITY OF SUCH DAMAGE. 27 */ 28 29 #include <sys/cdefs.h> 30 __RCSID("$NetBSD: t_dekker.c,v 1.3 2022/04/10 11:36:32 riastradh Exp $"); 31 32 #include <sys/atomic.h> 33 #include <sys/param.h> 34 #include <sys/sysctl.h> 35 36 #include <assert.h> 37 #include <atf-c.h> 38 #include <err.h> 39 #include <errno.h> 40 #include <inttypes.h> 41 #include <pthread.h> 42 #include <stdint.h> 43 #include <stdio.h> 44 #include <unistd.h> 45 46 #ifdef BROKEN_SYNC 47 #undef membar_sync 48 #define membar_sync() asm volatile("" ::: "memory") 49 #endif /* BROKEN_SYNC */ 50 51 volatile sig_atomic_t times_up; 52 53 volatile unsigned turn __aligned(COHERENCY_UNIT); 54 volatile struct { 55 unsigned v; 56 } __aligned(COHERENCY_UNIT) waiting[2]; 57 __CTASSERT(sizeof(waiting) == 2*COHERENCY_UNIT); 58 59 volatile uint64_t C; 60 uint64_t TC[2]; 61 62 static void 63 lock(unsigned me) 64 { 65 66 top: waiting[me].v = 1; 67 membar_sync(); 68 while (waiting[1 - me].v) { 69 if (turn != me) { 70 waiting[me].v = 0; 71 while (turn != me) 72 continue; 73 goto top; 74 } 75 } 76 membar_acquire(); 77 } 78 79 static void 80 unlock(unsigned me) 81 { 82 83 membar_release(); 84 turn = 1 - me; 85 waiting[me].v = 0; 86 87 /* 88 * Not needed for correctness, but this helps on Cavium Octeon 89 * cnMIPS CPUs which require issuing a sync plunger to unclog 90 * store buffers which can otherwise stay clogged for hundreds 91 * of thousands of cycles, giving very little concurrency to 92 * this test. 93 */ 94 membar_producer(); 95 } 96 97 static void * 98 thread(void *cookie) 99 { 100 unsigned me = (unsigned)(uintptr_t)cookie; 101 uint64_t C_local = 0; 102 103 while (!times_up) { 104 C_local++; 105 lock(me); 106 C++; 107 unlock(me); 108 } 109 110 TC[me] = C_local; 111 112 return NULL; 113 } 114 115 ATF_TC(dekker); 116 ATF_TC_HEAD(dekker, tc) 117 { 118 atf_tc_set_md_var(tc, "descr", 119 "Verify membar_sync works for Dekker's algorithm"); 120 } 121 ATF_TC_BODY(dekker, tc) 122 { 123 pthread_t t[2]; 124 unsigned i; 125 int ncpu; 126 size_t ncpulen = sizeof(ncpu); 127 int error; 128 129 alarm(10); 130 131 if (sysctlbyname("hw.ncpu", &ncpu, &ncpulen, NULL, 0) == -1) 132 atf_tc_fail("hw.ncpu: (%d) %s", errno, strerror(errno)); 133 assert(ncpulen == sizeof(ncpu)); 134 if (ncpu == 1) 135 atf_tc_skip("membar tests are only for multicore systems"); 136 137 for (i = 0; i < 2; i++) { 138 error = pthread_create(&t[i], NULL, &thread, 139 (void *)(uintptr_t)i); 140 if (error) 141 errc(1, error, "pthread_create"); 142 } 143 sleep(5); 144 times_up = 1; 145 for (i = 0; i < 2; i++) { 146 error = pthread_join(t[i], NULL); 147 if (error) 148 errc(1, error, "pthread_join"); 149 } 150 ATF_REQUIRE_MSG(C == TC[0] + TC[1], 151 "%"PRIu64" != %"PRIu64" + %"PRIu64" (off by %"PRIdMAX")", 152 C, TC[0], TC[1], TC[0] + TC[1] - C); 153 } 154 155 ATF_TP_ADD_TCS(tp) 156 { 157 158 ATF_TP_ADD_TC(tp, dekker); 159 return atf_no_error(); 160 } 161