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