arch/powerpc/kernel/smp-tbsync.c

   1 /*
   2  * Smp timebase synchronization for ppc.
   3  *
   4  * Copyright (C) 2003 Samuel Rydh (samuel@ibrium.se)
   5  *
   6  */
   7
   8 #include <linux/config.h>
   9 #include <linux/kernel.h>
  10 #include <linux/sched.h>
  11 #include <linux/smp.h>
  12 #include <linux/unistd.h>
  13 #include <linux/init.h>
  14 #include <asm/atomic.h>
  15 #include <asm/smp.h>
  16 #include <asm/time.h>
  17
  18 #define NUM_ITER                300
  19
  20 enum {
  21         kExit=0, kSetAndTest, kTest
  22 };
  23
  24 static struct {
  25         volatile u64            tb;
  26         volatile u64            mark;
  27         volatile int            cmd;
  28         volatile int            handshake;
  29         int                     filler[2];
  30
  31         volatile int            ack;
  32         int                     filler2[7];
  33
  34         volatile int            race_result;
  35 } *tbsync;
  36
  37 static volatile int             running;
  38
  39 static void __devinit enter_contest(u64 mark, long add)
  40 {
  41         while (get_tb() < mark)
  42                 tbsync->race_result = add;
  43 }
  44
  45 void __devinit smp_generic_take_timebase(void)
  46 {
  47         int cmd;
  48         u64 tb;
  49
  50         local_irq_disable();
  51         while (!running)
  52                 barrier();
  53         rmb();
  54
  55         for (;;) {
  56                 tbsync->ack = 1;
  57                 while (!tbsync->handshake)
  58                         barrier();
  59                 rmb();
  60
  61                 cmd = tbsync->cmd;
  62                 tb = tbsync->tb;
  63                 mb();
  64                 tbsync->ack = 0;
  65                 if (cmd == kExit)
  66                         break;
  67
  68                 while (tbsync->handshake)
  69                         barrier();
  70                 if (cmd == kSetAndTest)
  71                         set_tb(tb >> 32, tb & 0xfffffffful);
  72                 enter_contest(tbsync->mark, -1);
  73         }
  74         local_irq_enable();
  75 }
  76
  77 static int __devinit start_contest(int cmd, long offset, int num)
  78 {
  79         int i, score=0;
  80         u64 tb;
  81         long mark;
  82
  83         tbsync->cmd = cmd;
  84
  85         local_irq_disable();
  86         for (i = -3; i < num; ) {
  87                 tb = get_tb() + 400;
  88                 tbsync->tb = tb + offset;
  89                 tbsync->mark = mark = tb + 400;
  90
  91                 wmb();
  92
  93                 tbsync->handshake = 1;
  94                 while (tbsync->ack)
  95                         barrier();
  96
  97                 while (get_tb() <= tb)
  98                         barrier();
  99                 tbsync->handshake = 0;
 100                 enter_contest(mark, 1);
 101
 102                 while (!tbsync->ack)
 103                         barrier();
 104
 105                 if (i++ > 0)
 106                         score += tbsync->race_result;
 107         }
 108         local_irq_enable();
 109         return score;
 110 }
 111
 112 void __devinit smp_generic_give_timebase(void)
 113 {
 114         int i, score, score2, old, min=0, max=5000, offset=1000;
 115
 116         printk("Synchronizing timebase\n");
 117
 118         /* if this fails then this kernel won't work anyway... */
 119         tbsync = kmalloc( sizeof(*tbsync), GFP_KERNEL );
 120         memset( tbsync, 0, sizeof(*tbsync) );
 121         mb();
 122         running = 1;
 123
 124         while (!tbsync->ack)
 125                 barrier();
 126
 127         printk("Got ack\n");
 128
 129         /* binary search */
 130         for (old = -1; old != offset ; offset = (min+max) / 2) {
 131                 score = start_contest(kSetAndTest, offset, NUM_ITER);
 132
 133                 printk("score %d, offset %d\n", score, offset );
 134
 135                 if( score > 0 )
 136                         max = offset;
 137                 else
 138                         min = offset;
 139                 old = offset;
 140         }
 141         score = start_contest(kSetAndTest, min, NUM_ITER);
 142         score2 = start_contest(kSetAndTest, max, NUM_ITER);
 143
 144         printk("Min %d (score %d), Max %d (score %d)\n",
 145                min, score, max, score2);
 146         score = abs(score);
 147         score2 = abs(score2);
 148         offset = (score < score2) ? min : max;
 149
 150         /* guard against inaccurate mttb */
 151         for (i = 0; i < 10; i++) {
 152                 start_contest(kSetAndTest, offset, NUM_ITER/10);
 153
 154                 if ((score2 = start_contest(kTest, offset, NUM_ITER)) < 0)
 155                         score2 = -score2;
 156                 if (score2 <= score || score2 < 20)
 157                         break;
 158         }
 159         printk("Final offset: %d (%d/%d)\n", offset, score2, NUM_ITER );
 160
 161         /* exiting */
 162         tbsync->cmd = kExit;
 163         wmb();
 164         tbsync->handshake = 1;
 165         while (tbsync->ack)
 166                 barrier();
 167         tbsync->handshake = 0;
 168         kfree(tbsync);
 169         tbsync = NULL;
 170         running = 0;
 171 }