aboutsummaryrefslogtreecommitdiffstats
path: root/arch/powerpc/kernel/smp-tbsync.c
blob: 640de836e466eebd697acad630ed1d04f35a2f82 (plain) (blame)
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/kernel.h>
#include <linux/sched.h>
#include <linux/smp.h>
#include <linux/unistd.h>
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/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;
	unsigned long flags;

	local_irq_save(flags);
	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_restore(flags);
}

static int __devinit start_contest(int cmd, long offset, int num)
{
	int i, score=0;
	u64 tb;
	u64 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;

	pr_debug("Software timebase sync\n");

	/* if this fails then this kernel won't work anyway... */
	tbsync = kzalloc( sizeof(*tbsync), GFP_KERNEL );
	mb();
	running = 1;

	while (!tbsync->ack)
		barrier();

	pr_debug("Got ack\n");

	/* binary search */
	for (old = -1; old != offset ; offset = (min+max) / 2) {
		score = start_contest(kSetAndTest, offset, NUM_ITER);

		pr_debug("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);

	pr_debug("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;
	}
	pr_debug("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;
}