75 lines
1.9 KiB
C
75 lines
1.9 KiB
C
/*
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* sched_clock.c: support for extending counters to full 64-bit ns counter
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*/
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#include <linux/clocksource.h>
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#include <linux/init.h>
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#include <linux/jiffies.h>
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#include <linux/kernel.h>
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#include <linux/sched.h>
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#include <linux/timer.h>
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#include <asm/sched_clock.h>
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static void sched_clock_poll(unsigned long wrap_ticks);
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static DEFINE_TIMER(sched_clock_timer, sched_clock_poll, 0, 0);
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static void (*sched_clock_update_fn)(void);
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static void sched_clock_poll(unsigned long wrap_ticks)
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{
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mod_timer(&sched_clock_timer, round_jiffies(jiffies + wrap_ticks));
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sched_clock_update_fn();
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}
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void __init init_sched_clock(struct clock_data *cd, void (*update)(void),
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unsigned int clock_bits, unsigned long rate)
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{
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unsigned long r, w;
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u64 res, wrap;
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char r_unit;
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sched_clock_update_fn = update;
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/* calculate the mult/shift to convert counter ticks to ns. */
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clocks_calc_mult_shift(&cd->mult, &cd->shift, rate, NSEC_PER_SEC, 0);
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r = rate;
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if (r >= 4000000) {
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r /= 1000000;
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r_unit = 'M';
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} else {
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r /= 1000;
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r_unit = 'k';
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}
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/* calculate how many ns until we wrap */
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wrap = cyc_to_ns((1ULL << clock_bits) - 1, cd->mult, cd->shift);
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do_div(wrap, NSEC_PER_MSEC);
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w = wrap;
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/* calculate the ns resolution of this counter */
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res = cyc_to_ns(1ULL, cd->mult, cd->shift);
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pr_info("sched_clock: %u bits at %lu%cHz, resolution %lluns, wraps every %lums\n",
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clock_bits, r, r_unit, res, w);
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/*
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* Start the timer to keep sched_clock() properly updated and
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* sets the initial epoch.
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*/
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sched_clock_timer.data = msecs_to_jiffies(w - (w / 10));
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update();
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/*
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* Ensure that sched_clock() starts off at 0ns
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*/
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cd->epoch_ns = 0;
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}
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void __init sched_clock_postinit(void)
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{
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sched_clock_poll(sched_clock_timer.data);
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}
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