2 * sched_clock.c: support for extending counters to full 64-bit ns counter
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License version 2 as
6 * published by the Free Software Foundation.
8 #include <linux/clocksource.h>
9 #include <linux/init.h>
10 #include <linux/jiffies.h>
11 #include <linux/kernel.h>
12 #include <linux/sched.h>
13 #include <linux/syscore_ops.h>
14 #include <linux/timer.h>
16 #include <asm/sched_clock.h>
26 static void sched_clock_poll(unsigned long wrap_ticks
);
27 static DEFINE_TIMER(sched_clock_timer
, sched_clock_poll
, 0, 0);
29 static struct clock_data cd
= {
30 .mult
= NSEC_PER_SEC
/ HZ
,
33 static u32 __read_mostly sched_clock_mask
= 0xffffffff;
35 static u32 notrace
jiffy_sched_clock_read(void)
37 return (u32
)(jiffies
- INITIAL_JIFFIES
);
40 static u32
__read_mostly (*read_sched_clock
)(void) = jiffy_sched_clock_read
;
42 static inline u64
cyc_to_ns(u64 cyc
, u32 mult
, u32 shift
)
44 return (cyc
* mult
) >> shift
;
47 static unsigned long long cyc_to_sched_clock(u32 cyc
, u32 mask
)
53 * Load the epoch_cyc and epoch_ns atomically. We do this by
54 * ensuring that we always write epoch_cyc, epoch_ns and
55 * epoch_cyc_copy in strict order, and read them in strict order.
56 * If epoch_cyc and epoch_cyc_copy are not equal, then we're in
57 * the middle of an update, and we should repeat the load.
60 epoch_cyc
= cd
.epoch_cyc
;
62 epoch_ns
= cd
.epoch_ns
;
64 } while (epoch_cyc
!= cd
.epoch_cyc_copy
);
66 return epoch_ns
+ cyc_to_ns((cyc
- epoch_cyc
) & mask
, cd
.mult
, cd
.shift
);
70 * Atomically update the sched_clock epoch.
72 static void notrace
update_sched_clock(void)
78 cyc
= read_sched_clock();
80 cyc_to_ns((cyc
- cd
.epoch_cyc
) & sched_clock_mask
,
83 * Write epoch_cyc and epoch_ns in a way that the update is
84 * detectable in cyc_to_fixed_sched_clock().
86 raw_local_irq_save(flags
);
91 cd
.epoch_cyc_copy
= cyc
;
92 raw_local_irq_restore(flags
);
95 static void sched_clock_poll(unsigned long wrap_ticks
)
97 mod_timer(&sched_clock_timer
, round_jiffies(jiffies
+ wrap_ticks
));
101 void __init
setup_sched_clock(u32 (*read
)(void), int bits
, unsigned long rate
)
108 WARN_ON(!irqs_disabled());
109 WARN_ON(read_sched_clock
!= jiffy_sched_clock_read
);
110 read_sched_clock
= read
;
111 sched_clock_mask
= (1 << bits
) - 1;
113 /* calculate the mult/shift to convert counter ticks to ns. */
114 clocks_calc_mult_shift(&cd
.mult
, &cd
.shift
, rate
, NSEC_PER_SEC
, 0);
120 } else if (r
>= 1000) {
126 /* calculate how many ns until we wrap */
127 wrap
= cyc_to_ns((1ULL << bits
) - 1, cd
.mult
, cd
.shift
);
128 do_div(wrap
, NSEC_PER_MSEC
);
131 /* calculate the ns resolution of this counter */
132 res
= cyc_to_ns(1ULL, cd
.mult
, cd
.shift
);
133 pr_info("sched_clock: %u bits at %lu%cHz, resolution %lluns, wraps every %lums\n",
134 bits
, r
, r_unit
, res
, w
);
137 * Start the timer to keep sched_clock() properly updated and
138 * sets the initial epoch.
140 sched_clock_timer
.data
= msecs_to_jiffies(w
- (w
/ 10));
141 update_sched_clock();
144 * Ensure that sched_clock() starts off at 0ns
148 pr_debug("Registered %pF as sched_clock source\n", read
);
151 unsigned long long notrace
sched_clock(void)
153 u32 cyc
= read_sched_clock();
154 return cyc_to_sched_clock(cyc
, sched_clock_mask
);
157 void __init
sched_clock_postinit(void)
160 * If no sched_clock function has been provided at that point,
161 * make it the final one one.
163 if (read_sched_clock
== jiffy_sched_clock_read
)
164 setup_sched_clock(jiffy_sched_clock_read
, 32, HZ
);
166 sched_clock_poll(sched_clock_timer
.data
);
169 static int sched_clock_suspend(void)
171 sched_clock_poll(sched_clock_timer
.data
);
175 static struct syscore_ops sched_clock_ops
= {
176 .suspend
= sched_clock_suspend
,
179 static int __init
sched_clock_syscore_init(void)
181 register_syscore_ops(&sched_clock_ops
);
184 device_initcall(sched_clock_syscore_init
);