| 1 | /* |
| 2 | * test-read-lock-speed.c |
| 3 | * |
| 4 | * Compare speed of : |
| 5 | * - spin lock irqsave / spin unlock irqrestore (close to rwlocks when |
| 6 | * uncontended) |
| 7 | * - using a sequence read lock (uncontended) |
| 8 | * - preempt disable/enable (RCU) |
| 9 | * |
| 10 | * Copyright 2009 - Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> |
| 11 | * Distributed under GPLv2 |
| 12 | */ |
| 13 | |
| 14 | #include <linux/jiffies.h> |
| 15 | #include <linux/compiler.h> |
| 16 | #include <linux/init.h> |
| 17 | #include <linux/module.h> |
| 18 | #include <linux/math64.h> |
| 19 | #include <linux/spinlock.h> |
| 20 | #include <linux/seqlock.h> |
| 21 | #include <linux/cpumask.h> |
| 22 | #include <asm/timex.h> |
| 23 | #include <asm/system.h> |
| 24 | |
| 25 | #define NR_LOOPS 20000 |
| 26 | |
| 27 | #ifndef CONFIG_PREEMPT |
| 28 | #error "Your kernel should be build with preemption enabled" |
| 29 | #endif |
| 30 | |
| 31 | #ifdef CONFIG_DEBUG_PREEMPT |
| 32 | #error "Please disable CONFIG_DEBUG_PREEMPT" |
| 33 | #endif |
| 34 | |
| 35 | #ifdef CONFIG_DEBUG_SPINLOCK |
| 36 | #error "Please disable CONFIG_DEBUG_SPINLOCK" |
| 37 | #endif |
| 38 | |
| 39 | #ifdef CONFIG_LOCKDEP |
| 40 | #error "Please disable CONFIG_LOCKDEP" |
| 41 | #endif |
| 42 | |
| 43 | int test_val; |
| 44 | |
| 45 | static void do_testbaseline(void) |
| 46 | { |
| 47 | unsigned long flags; |
| 48 | unsigned int i; |
| 49 | cycles_t time1, time2, time; |
| 50 | u32 rem; |
| 51 | |
| 52 | local_irq_save(flags); |
| 53 | preempt_disable(); |
| 54 | time1 = get_cycles(); |
| 55 | for (i = 0; i < NR_LOOPS; i++) { |
| 56 | asm volatile (""); |
| 57 | } |
| 58 | time2 = get_cycles(); |
| 59 | local_irq_restore(flags); |
| 60 | preempt_enable(); |
| 61 | time = time2 - time1; |
| 62 | |
| 63 | printk(KERN_ALERT "test results: time for baseline\n"); |
| 64 | printk(KERN_ALERT "number of loops: %d\n", NR_LOOPS); |
| 65 | printk(KERN_ALERT "total time: %llu\n", time); |
| 66 | time = div_u64_rem(time, NR_LOOPS, &rem); |
| 67 | printk(KERN_ALERT "-> baseline takes %llu cycles\n", time); |
| 68 | printk(KERN_ALERT "test end\n"); |
| 69 | } |
| 70 | |
| 71 | static void do_test_spinlock(void) |
| 72 | { |
| 73 | static DEFINE_SPINLOCK(mylock); |
| 74 | unsigned long flags; |
| 75 | unsigned int i; |
| 76 | cycles_t time1, time2, time; |
| 77 | u32 rem; |
| 78 | |
| 79 | preempt_disable(); |
| 80 | spin_lock_irqsave(&mylock, flags); |
| 81 | time1 = get_cycles(); |
| 82 | for (i = 0; i < NR_LOOPS; i++) { |
| 83 | spin_unlock(&mylock); |
| 84 | spin_lock(&mylock); |
| 85 | } |
| 86 | time2 = get_cycles(); |
| 87 | spin_unlock_irqrestore(&mylock, flags); |
| 88 | preempt_enable(); |
| 89 | time = time2 - time1; |
| 90 | |
| 91 | printk(KERN_ALERT "test results: time for spinlock\n"); |
| 92 | printk(KERN_ALERT "number of loops: %d\n", NR_LOOPS); |
| 93 | printk(KERN_ALERT "total time: %llu\n", time); |
| 94 | time = div_u64_rem(time, NR_LOOPS, &rem); |
| 95 | printk(KERN_ALERT "-> spinlock takes %llu cycles\n", time); |
| 96 | printk(KERN_ALERT "test end\n"); |
| 97 | } |
| 98 | |
| 99 | static void do_test_seqlock(void) |
| 100 | { |
| 101 | static seqlock_t test_lock; |
| 102 | unsigned long seq; |
| 103 | unsigned long flags; |
| 104 | unsigned int i; |
| 105 | cycles_t time1, time2, time; |
| 106 | u32 rem; |
| 107 | |
| 108 | local_irq_save(flags); |
| 109 | time1 = get_cycles(); |
| 110 | for (i = 0; i < NR_LOOPS; i++) { |
| 111 | do { |
| 112 | seq = read_seqbegin(&test_lock); |
| 113 | } while (read_seqretry(&test_lock, seq)); |
| 114 | } |
| 115 | time2 = get_cycles(); |
| 116 | time = time2 - time1; |
| 117 | local_irq_restore(flags); |
| 118 | |
| 119 | printk(KERN_ALERT "test results: time for seqlock\n"); |
| 120 | printk(KERN_ALERT "number of loops: %d\n", NR_LOOPS); |
| 121 | printk(KERN_ALERT "total time: %llu\n", time); |
| 122 | time = div_u64_rem(time, NR_LOOPS, &rem); |
| 123 | printk(KERN_ALERT "-> seqlock takes %llu cycles\n", time); |
| 124 | printk(KERN_ALERT "test end\n"); |
| 125 | } |
| 126 | |
| 127 | /* |
| 128 | * Note : This test _should_ trigger lockdep errors due to preemption |
| 129 | * disabling/enabling within irq off section. Given we are only interested in |
| 130 | * having the most precise measurement for preemption disable/enable, we don't |
| 131 | * care about this. |
| 132 | */ |
| 133 | static void do_test_preempt(void) |
| 134 | { |
| 135 | unsigned long flags; |
| 136 | unsigned int i; |
| 137 | cycles_t time1, time2, time; |
| 138 | u32 rem; |
| 139 | |
| 140 | local_irq_save(flags); |
| 141 | preempt_disable(); |
| 142 | time1 = get_cycles(); |
| 143 | for (i = 0; i < NR_LOOPS; i++) { |
| 144 | preempt_disable(); |
| 145 | preempt_enable(); |
| 146 | } |
| 147 | time2 = get_cycles(); |
| 148 | preempt_enable(); |
| 149 | time = time2 - time1; |
| 150 | local_irq_restore(flags); |
| 151 | |
| 152 | printk(KERN_ALERT |
| 153 | "test results: time for preempt disable/enable pairs\n"); |
| 154 | printk(KERN_ALERT "number of loops: %d\n", NR_LOOPS); |
| 155 | printk(KERN_ALERT "total time: %llu\n", time); |
| 156 | time = div_u64_rem(time, NR_LOOPS, &rem); |
| 157 | printk(KERN_ALERT "-> preempt disable/enable pair takes %llu cycles\n", |
| 158 | time); |
| 159 | printk(KERN_ALERT "test end\n"); |
| 160 | } |
| 161 | |
| 162 | static int ltt_test_init(void) |
| 163 | { |
| 164 | printk(KERN_ALERT "test init\n"); |
| 165 | |
| 166 | printk(KERN_ALERT "Number of active CPUs : %d\n", num_online_cpus()); |
| 167 | do_testbaseline(); |
| 168 | do_test_spinlock(); |
| 169 | do_test_seqlock(); |
| 170 | do_test_preempt(); |
| 171 | return -EAGAIN; /* Fail will directly unload the module */ |
| 172 | } |
| 173 | |
| 174 | static void ltt_test_exit(void) |
| 175 | { |
| 176 | printk(KERN_ALERT "test exit\n"); |
| 177 | } |
| 178 | |
| 179 | module_init(ltt_test_init) |
| 180 | module_exit(ltt_test_exit) |
| 181 | |
| 182 | MODULE_LICENSE("GPL"); |
| 183 | MODULE_AUTHOR("Mathieu Desnoyers"); |
| 184 | MODULE_DESCRIPTION("Test read lock speed"); |