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
172
173
174
175
176
177
178
179
180
181
182
183
184
|
/*
* sched_clock.c: support for extending counters to full 64-bit ns counter
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/
#include <linux/clocksource.h>
#include <linux/init.h>
#include <linux/jiffies.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/syscore_ops.h>
#include <linux/timer.h>
#include <asm/sched_clock.h>
struct clock_data {
u64 epoch_ns;
u32 epoch_cyc;
u32 epoch_cyc_copy;
u32 mult;
u32 shift;
};
static void sched_clock_poll(unsigned long wrap_ticks);
static DEFINE_TIMER(sched_clock_timer, sched_clock_poll, 0, 0);
static struct clock_data cd = {
.mult = NSEC_PER_SEC / HZ,
};
static u32 __read_mostly sched_clock_mask = 0xffffffff;
static u32 notrace jiffy_sched_clock_read(void)
{
return (u32)(jiffies - INITIAL_JIFFIES);
}
static u32 __read_mostly (*read_sched_clock)(void) = jiffy_sched_clock_read;
static inline u64 cyc_to_ns(u64 cyc, u32 mult, u32 shift)
{
return (cyc * mult) >> shift;
}
static unsigned long long cyc_to_sched_clock(u32 cyc, u32 mask)
{
u64 epoch_ns;
u32 epoch_cyc;
/*
* Load the epoch_cyc and epoch_ns atomically. We do this by
* ensuring that we always write epoch_cyc, epoch_ns and
* epoch_cyc_copy in strict order, and read them in strict order.
* If epoch_cyc and epoch_cyc_copy are not equal, then we're in
* the middle of an update, and we should repeat the load.
*/
do {
epoch_cyc = cd.epoch_cyc;
smp_rmb();
epoch_ns = cd.epoch_ns;
smp_rmb();
} while (epoch_cyc != cd.epoch_cyc_copy);
return epoch_ns + cyc_to_ns((cyc - epoch_cyc) & mask, cd.mult, cd.shift);
}
/*
* Atomically update the sched_clock epoch.
*/
static void notrace update_sched_clock(void)
{
unsigned long flags;
u32 cyc;
u64 ns;
cyc = read_sched_clock();
ns = cd.epoch_ns +
cyc_to_ns((cyc - cd.epoch_cyc) & sched_clock_mask,
cd.mult, cd.shift);
/*
* Write epoch_cyc and epoch_ns in a way that the update is
* detectable in cyc_to_fixed_sched_clock().
*/
raw_local_irq_save(flags);
cd.epoch_cyc = cyc;
smp_wmb();
cd.epoch_ns = ns;
smp_wmb();
cd.epoch_cyc_copy = cyc;
raw_local_irq_restore(flags);
}
static void sched_clock_poll(unsigned long wrap_ticks)
{
mod_timer(&sched_clock_timer, round_jiffies(jiffies + wrap_ticks));
update_sched_clock();
}
void __init setup_sched_clock(u32 (*read)(void), int bits, unsigned long rate)
{
unsigned long r, w;
u64 res, wrap;
char r_unit;
BUG_ON(bits > 32);
WARN_ON(!irqs_disabled());
WARN_ON(read_sched_clock != jiffy_sched_clock_read);
read_sched_clock = read;
sched_clock_mask = (1 << bits) - 1;
/* calculate the mult/shift to convert counter ticks to ns. */
clocks_calc_mult_shift(&cd.mult, &cd.shift, rate, NSEC_PER_SEC, 0);
r = rate;
if (r >= 4000000) {
r /= 1000000;
r_unit = 'M';
} else if (r >= 1000) {
r /= 1000;
r_unit = 'k';
} else
r_unit = ' ';
/* calculate how many ns until we wrap */
wrap = cyc_to_ns((1ULL << bits) - 1, cd.mult, cd.shift);
do_div(wrap, NSEC_PER_MSEC);
w = wrap;
/* calculate the ns resolution of this counter */
res = cyc_to_ns(1ULL, cd.mult, cd.shift);
pr_info("sched_clock: %u bits at %lu%cHz, resolution %lluns, wraps every %lums\n",
bits, r, r_unit, res, w);
/*
* Start the timer to keep sched_clock() properly updated and
* sets the initial epoch.
*/
sched_clock_timer.data = msecs_to_jiffies(w - (w / 10));
update_sched_clock();
/*
* Ensure that sched_clock() starts off at 0ns
*/
cd.epoch_ns = 0;
pr_debug("Registered %pF as sched_clock source\n", read);
}
unsigned long long notrace sched_clock(void)
{
u32 cyc = read_sched_clock();
return cyc_to_sched_clock(cyc, sched_clock_mask);
}
void __init sched_clock_postinit(void)
{
/*
* If no sched_clock function has been provided at that point,
* make it the final one one.
*/
if (read_sched_clock == jiffy_sched_clock_read)
setup_sched_clock(jiffy_sched_clock_read, 32, HZ);
sched_clock_poll(sched_clock_timer.data);
}
static int sched_clock_suspend(void)
{
sched_clock_poll(sched_clock_timer.data);
return 0;
}
static struct syscore_ops sched_clock_ops = {
.suspend = sched_clock_suspend,
};
static int __init sched_clock_syscore_init(void)
{
register_syscore_ops(&sched_clock_ops);
return 0;
}
device_initcall(sched_clock_syscore_init);
|
