tests/kernel/test-cmpxchg-nolock2.c

   1 /* test-cmpxchg-nolock.c
   2  *
   3  * Compare local cmpxchg with irq disable / enable.
   4  */
   5
   6
   7 #include <linux/jiffies.h>
   8 #include <linux/compiler.h>
   9 #include <linux/init.h>
  10 #include <linux/module.h>
  11 #include <linux/calc64.h>
  12 #include <asm/timex.h>
  13 #include <asm/system.h>
  14
  15 #define NR_LOOPS 20000
  16
  17 int test_val;
  18
  19 static void do_test_cmpxchg(void)
  20 {
  21         int ret;
  22         long flags;
  23         unsigned int i;
  24         cycles_t time1, time2, time;
  25         long rem;
  26
  27         local_irq_save(flags);
  28         preempt_disable();
  29         time1 = get_cycles();
  30         for (i = 0; i < NR_LOOPS; i++) {
  31                 ret = cmpxchg_local(&test_val, 0, 0);
  32         }
  33         time2 = get_cycles();
  34         local_irq_restore(flags);
  35         preempt_enable();
  36         time = time2 - time1;
  37
  38         printk(KERN_ALERT "test results: time for non locked cmpxchg\n");
  39         printk(KERN_ALERT "number of loops: %d\n", NR_LOOPS);
  40         printk(KERN_ALERT "total time: %llu\n", time);
  41         time = div_long_long_rem(time, NR_LOOPS, &rem);
  42         printk(KERN_ALERT "-> non locked cmpxchg takes %llu cycles\n", time);
  43         printk(KERN_ALERT "test end\n");
  44 }
  45
  46 /*
  47  * This test will have a higher standard deviation due to incoming interrupts.
  48  */
  49 static void do_test_enable_int(void)
  50 {
  51         long flags;
  52         unsigned int i;
  53         cycles_t time1, time2, time;
  54         long rem;
  55
  56         local_irq_save(flags);
  57         preempt_disable();
  58         time1 = get_cycles();
  59         for (i = 0; i < NR_LOOPS; i++) {
  60                 local_irq_restore(flags);
  61         }
  62         time2 = get_cycles();
  63         local_irq_restore(flags);
  64         preempt_enable();
  65         time = time2 - time1;
  66
  67         printk(KERN_ALERT "test results: time for enabling interrupts (STI)\n");
  68         printk(KERN_ALERT "number of loops: %d\n", NR_LOOPS);
  69         printk(KERN_ALERT "total time: %llu\n", time);
  70         time = div_long_long_rem(time, NR_LOOPS, &rem);
  71         printk(KERN_ALERT "-> enabling interrupts (STI) takes %llu cycles\n",
  72                                         time);
  73         printk(KERN_ALERT "test end\n");
  74 }
  75
  76 static void do_test_disable_int(void)
  77 {
  78         unsigned long flags, flags2;
  79         unsigned int i;
  80         cycles_t time1, time2, time;
  81         long rem;
  82
  83         local_irq_save(flags);
  84         preempt_disable();
  85         time1 = get_cycles();
  86         for ( i = 0; i < NR_LOOPS; i++) {
  87                 local_irq_save(flags2);
  88         }
  89         time2 = get_cycles();
  90         local_irq_restore(flags);
  91         preempt_enable();
  92         time = time2 - time1;
  93
  94         printk(KERN_ALERT "test results: time for disabling interrupts (CLI)\n");
  95         printk(KERN_ALERT "number of loops: %d\n", NR_LOOPS);
  96         printk(KERN_ALERT "total time: %llu\n", time);
  97         time = div_long_long_rem(time, NR_LOOPS, &rem);
  98         printk(KERN_ALERT "-> disabling interrupts (CLI) takes %llu cycles\n",
  99                                 time);
 100         printk(KERN_ALERT "test end\n");
 101 }
 102
 103
 104
 105 static int ltt_test_init(void)
 106 {
 107         printk(KERN_ALERT "test init\n");
 108
 109         do_test_cmpxchg();
 110         do_test_enable_int();
 111         do_test_disable_int();
 112         return -EAGAIN; /* Fail will directly unload the module */
 113 }
 114
 115 static void ltt_test_exit(void)
 116 {
 117         printk(KERN_ALERT "test exit\n");
 118 }
 119
 120 module_init(ltt_test_init)
 121 module_exit(ltt_test_exit)
 122
 123 MODULE_LICENSE("GPL");
 124 MODULE_AUTHOR("Mathieu Desnoyers");
 125 MODULE_DESCRIPTION("Cmpxchg vs int Test");
 126