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112f38a4 RK |
1 | /* |
2 | * sched_clock.c: support for extending counters to full 64-bit ns counter | |
3 | * | |
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. | |
7 | */ | |
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/timer.h> | |
14 | ||
15 | #include <asm/sched_clock.h> | |
16 | ||
17 | static void sched_clock_poll(unsigned long wrap_ticks); | |
18 | static DEFINE_TIMER(sched_clock_timer, sched_clock_poll, 0, 0); | |
19 | static void (*sched_clock_update_fn)(void); | |
20 | ||
21 | static void sched_clock_poll(unsigned long wrap_ticks) | |
22 | { | |
23 | mod_timer(&sched_clock_timer, round_jiffies(jiffies + wrap_ticks)); | |
24 | sched_clock_update_fn(); | |
25 | } | |
26 | ||
27 | void __init init_sched_clock(struct clock_data *cd, void (*update)(void), | |
28 | unsigned int clock_bits, unsigned long rate) | |
29 | { | |
30 | unsigned long r, w; | |
31 | u64 res, wrap; | |
32 | char r_unit; | |
33 | ||
34 | sched_clock_update_fn = update; | |
35 | ||
36 | /* calculate the mult/shift to convert counter ticks to ns. */ | |
37 | clocks_calc_mult_shift(&cd->mult, &cd->shift, rate, NSEC_PER_SEC, 60); | |
38 | ||
39 | r = rate; | |
40 | if (r >= 4000000) { | |
41 | r /= 1000000; | |
42 | r_unit = 'M'; | |
43 | } else { | |
44 | r /= 1000; | |
45 | r_unit = 'k'; | |
46 | } | |
47 | ||
48 | /* calculate how many ns until we wrap */ | |
49 | wrap = cyc_to_ns((1ULL << clock_bits) - 1, cd->mult, cd->shift); | |
50 | do_div(wrap, NSEC_PER_MSEC); | |
51 | w = wrap; | |
52 | ||
53 | /* calculate the ns resolution of this counter */ | |
54 | res = cyc_to_ns(1ULL, cd->mult, cd->shift); | |
55 | pr_info("sched_clock: %u bits at %lu%cHz, resolution %lluns, wraps every %lums\n", | |
56 | clock_bits, r, r_unit, res, w); | |
57 | ||
58 | /* | |
59 | * Start the timer to keep sched_clock() properly updated and | |
60 | * sets the initial epoch. | |
61 | */ | |
62 | sched_clock_timer.data = msecs_to_jiffies(w - (w / 10)); | |
63 | sched_clock_poll(sched_clock_timer.data); | |
64 | ||
65 | /* | |
66 | * Ensure that sched_clock() starts off at 0ns | |
67 | */ | |
68 | cd->epoch_ns = 0; | |
69 | } |