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32 results

sched_clock.c

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    Ben Dooks (Codethink) authored and Thomas Gleixner committed
    Include the timekeeping.h header to get the declaration of the
    sched_clock_{suspend,resume} functions. Fixes the following sparse
    warnings:
    
    kernel/time/sched_clock.c:275:5: warning: symbol 'sched_clock_suspend' was not declared. Should it be static?
    kernel/time/sched_clock.c:286:6: warning: symbol 'sched_clock_resume' was not declared. Should it be static?
    
    Signed-off-by: default avatarBen Dooks (Codethink) <ben.dooks@codethink.co.uk>
    Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
    Link: https://lkml.kernel.org/r/20191022131226.11465-1-ben.dooks@codethink.co.uk
    086ee46b
    History
    sched_clock.c 8.13 KiB
    // SPDX-License-Identifier: GPL-2.0
    /*
     * Generic sched_clock() support, to extend low level hardware time
     * counters to full 64-bit ns values.
     */
    #include <linux/clocksource.h>
    #include <linux/init.h>
    #include <linux/jiffies.h>
    #include <linux/ktime.h>
    #include <linux/kernel.h>
    #include <linux/moduleparam.h>
    #include <linux/sched.h>
    #include <linux/sched/clock.h>
    #include <linux/syscore_ops.h>
    #include <linux/hrtimer.h>
    #include <linux/sched_clock.h>
    #include <linux/seqlock.h>
    #include <linux/bitops.h>
    
    #include "timekeeping.h"
    
    /**
     * struct clock_read_data - data required to read from sched_clock()
     *
     * @epoch_ns:		sched_clock() value at last update
     * @epoch_cyc:		Clock cycle value at last update.
     * @sched_clock_mask:   Bitmask for two's complement subtraction of non 64bit
     *			clocks.
     * @read_sched_clock:	Current clock source (or dummy source when suspended).
     * @mult:		Multipler for scaled math conversion.
     * @shift:		Shift value for scaled math conversion.
     *
     * Care must be taken when updating this structure; it is read by
     * some very hot code paths. It occupies <=40 bytes and, when combined
     * with the seqcount used to synchronize access, comfortably fits into
     * a 64 byte cache line.
     */
    struct clock_read_data {
    	u64 epoch_ns;
    	u64 epoch_cyc;
    	u64 sched_clock_mask;
    	u64 (*read_sched_clock)(void);
    	u32 mult;
    	u32 shift;
    };
    
    /**
     * struct clock_data - all data needed for sched_clock() (including
     *                     registration of a new clock source)
     *
     * @seq:		Sequence counter for protecting updates. The lowest
     *			bit is the index for @read_data.
     * @read_data:		Data required to read from sched_clock.
     * @wrap_kt:		Duration for which clock can run before wrapping.
     * @rate:		Tick rate of the registered clock.
     * @actual_read_sched_clock: Registered hardware level clock read function.
     *
     * The ordering of this structure has been chosen to optimize cache
     * performance. In particular 'seq' and 'read_data[0]' (combined) should fit
     * into a single 64-byte cache line.
     */
    struct clock_data {
    	seqcount_t		seq;
    	struct clock_read_data	read_data[2];
    	ktime_t			wrap_kt;
    	unsigned long		rate;
    
    	u64 (*actual_read_sched_clock)(void);
    };
    
    static struct hrtimer sched_clock_timer;
    static int irqtime = -1;
    
    core_param(irqtime, irqtime, int, 0400);
    
    static u64 notrace jiffy_sched_clock_read(void)
    {
    	/*
    	 * We don't need to use get_jiffies_64 on 32-bit arches here
    	 * because we register with BITS_PER_LONG
    	 */
    	return (u64)(jiffies - INITIAL_JIFFIES);
    }
    
    static struct clock_data cd ____cacheline_aligned = {
    	.read_data[0] = { .mult = NSEC_PER_SEC / HZ,
    			  .read_sched_clock = jiffy_sched_clock_read, },
    	.actual_read_sched_clock = jiffy_sched_clock_read,
    };
    
    static inline u64 notrace cyc_to_ns(u64 cyc, u32 mult, u32 shift)
    {
    	return (cyc * mult) >> shift;
    }
    
    unsigned long long notrace sched_clock(void)
    {
    	u64 cyc, res;
    	unsigned int seq;
    	struct clock_read_data *rd;
    
    	do {
    		seq = raw_read_seqcount(&cd.seq);
    		rd = cd.read_data + (seq & 1);
    
    		cyc = (rd->read_sched_clock() - rd->epoch_cyc) &
    		      rd->sched_clock_mask;
    		res = rd->epoch_ns + cyc_to_ns(cyc, rd->mult, rd->shift);
    	} while (read_seqcount_retry(&cd.seq, seq));
    
    	return res;
    }
    
    /*
     * Updating the data required to read the clock.
     *
     * sched_clock() will never observe mis-matched data even if called from
     * an NMI. We do this by maintaining an odd/even copy of the data and
     * steering sched_clock() to one or the other using a sequence counter.
     * In order to preserve the data cache profile of sched_clock() as much
     * as possible the system reverts back to the even copy when the update
     * completes; the odd copy is used *only* during an update.
     */
    static void update_clock_read_data(struct clock_read_data *rd)
    {
    	/* update the backup (odd) copy with the new data */
    	cd.read_data[1] = *rd;
    
    	/* steer readers towards the odd copy */
    	raw_write_seqcount_latch(&cd.seq);
    
    	/* now its safe for us to update the normal (even) copy */
    	cd.read_data[0] = *rd;
    
    	/* switch readers back to the even copy */
    	raw_write_seqcount_latch(&cd.seq);
    }
    
    /*
     * Atomically update the sched_clock() epoch.
     */
    static void update_sched_clock(void)
    {
    	u64 cyc;
    	u64 ns;
    	struct clock_read_data rd;
    
    	rd = cd.read_data[0];
    
    	cyc = cd.actual_read_sched_clock();
    	ns = rd.epoch_ns + cyc_to_ns((cyc - rd.epoch_cyc) & rd.sched_clock_mask, rd.mult, rd.shift);
    
    	rd.epoch_ns = ns;
    	rd.epoch_cyc = cyc;
    
    	update_clock_read_data(&rd);
    }
    
    static enum hrtimer_restart sched_clock_poll(struct hrtimer *hrt)
    {
    	update_sched_clock();
    	hrtimer_forward_now(hrt, cd.wrap_kt);
    
    	return HRTIMER_RESTART;
    }
    
    void __init
    sched_clock_register(u64 (*read)(void), int bits, unsigned long rate)
    {
    	u64 res, wrap, new_mask, new_epoch, cyc, ns;
    	u32 new_mult, new_shift;
    	unsigned long r;
    	char r_unit;
    	struct clock_read_data rd;
    
    	if (cd.rate > rate)
    		return;
    
    	WARN_ON(!irqs_disabled());
    
    	/* Calculate the mult/shift to convert counter ticks to ns. */
    	clocks_calc_mult_shift(&new_mult, &new_shift, rate, NSEC_PER_SEC, 3600);
    
    	new_mask = CLOCKSOURCE_MASK(bits);
    	cd.rate = rate;
    
    	/* Calculate how many nanosecs until we risk wrapping */
    	wrap = clocks_calc_max_nsecs(new_mult, new_shift, 0, new_mask, NULL);
    	cd.wrap_kt = ns_to_ktime(wrap);
    
    	rd = cd.read_data[0];
    
    	/* Update epoch for new counter and update 'epoch_ns' from old counter*/
    	new_epoch = read();
    	cyc = cd.actual_read_sched_clock();
    	ns = rd.epoch_ns + cyc_to_ns((cyc - rd.epoch_cyc) & rd.sched_clock_mask, rd.mult, rd.shift);
    	cd.actual_read_sched_clock = read;
    
    	rd.read_sched_clock	= read;
    	rd.sched_clock_mask	= new_mask;
    	rd.mult			= new_mult;
    	rd.shift		= new_shift;
    	rd.epoch_cyc		= new_epoch;
    	rd.epoch_ns		= ns;
    
    	update_clock_read_data(&rd);
    
    	if (sched_clock_timer.function != NULL) {
    		/* update timeout for clock wrap */
    		hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL);
    	}
    
    	r = rate;
    	if (r >= 4000000) {
    		r /= 1000000;
    		r_unit = 'M';
    	} else {
    		if (r >= 1000) {
    			r /= 1000;
    			r_unit = 'k';
    		} else {
    			r_unit = ' ';
    		}
    	}
    
    	/* Calculate the ns resolution of this counter */
    	res = cyc_to_ns(1ULL, new_mult, new_shift);
    
    	pr_info("sched_clock: %u bits at %lu%cHz, resolution %lluns, wraps every %lluns\n",
    		bits, r, r_unit, res, wrap);
    
    	/* Enable IRQ time accounting if we have a fast enough sched_clock() */
    	if (irqtime > 0 || (irqtime == -1 && rate >= 1000000))
    		enable_sched_clock_irqtime();
    
    	pr_debug("Registered %pS as sched_clock source\n", read);
    }
    
    void __init generic_sched_clock_init(void)
    {
    	/*
    	 * If no sched_clock() function has been provided at that point,
    	 * make it the final one one.
    	 */
    	if (cd.actual_read_sched_clock == jiffy_sched_clock_read)
    		sched_clock_register(jiffy_sched_clock_read, BITS_PER_LONG, HZ);
    
    	update_sched_clock();
    
    	/*
    	 * Start the timer to keep sched_clock() properly updated and
    	 * sets the initial epoch.
    	 */
    	hrtimer_init(&sched_clock_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
    	sched_clock_timer.function = sched_clock_poll;
    	hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL);
    }
    
    /*
     * Clock read function for use when the clock is suspended.
     *
     * This function makes it appear to sched_clock() as if the clock
     * stopped counting at its last update.
     *
     * This function must only be called from the critical
     * section in sched_clock(). It relies on the read_seqcount_retry()
     * at the end of the critical section to be sure we observe the
     * correct copy of 'epoch_cyc'.
     */
    static u64 notrace suspended_sched_clock_read(void)
    {
    	unsigned int seq = raw_read_seqcount(&cd.seq);
    
    	return cd.read_data[seq & 1].epoch_cyc;
    }
    
    int sched_clock_suspend(void)
    {
    	struct clock_read_data *rd = &cd.read_data[0];
    
    	update_sched_clock();
    	hrtimer_cancel(&sched_clock_timer);
    	rd->read_sched_clock = suspended_sched_clock_read;
    
    	return 0;
    }
    
    void sched_clock_resume(void)
    {
    	struct clock_read_data *rd = &cd.read_data[0];
    
    	rd->epoch_cyc = cd.actual_read_sched_clock();
    	hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL);
    	rd->read_sched_clock = cd.actual_read_sched_clock;
    }
    
    static struct syscore_ops sched_clock_ops = {
    	.suspend	= sched_clock_suspend,
    	.resume		= sched_clock_resume,
    };
    
    static int __init sched_clock_syscore_init(void)
    {
    	register_syscore_ops(&sched_clock_ops);
    
    	return 0;
    }
    device_initcall(sched_clock_syscore_init);