Commit 32fea568 authored by Ingo Molnar's avatar Ingo Molnar
Browse files

timers, sched/clock: Clean up the code a bit 



Trivial cleanups, to improve the readability of the generic sched_clock() code:

 - Improve and standardize comments
 - Standardize the coding style
 - Use vertical spacing where appropriate
 - etc.

No code changed:

  md5:
    19a053b31e0c54feaeff1492012b019a  sched_clock.o.before.asm
    19a053b31e0c54feaeff1492012b019a  sched_clock.o.after.asm

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Daniel Thompson <daniel.thompson@linaro.org>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Stephen Boyd <sboyd@codeaurora.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 1809bfa4

kernel/time/sched_clock.c

+56 −51
Original line number Diff line number Diff line 
/*

 * sched_clock.c: support for extending counters to full 64-bit ns counter

 * sched_clock.c: Generic sched_clock() support, to extend low level

 *                hardware time counters to full 64-bit ns values.

 *

 * 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
@@ -19,15 +20,15 @@ 
#include <linux/bitops.h>



/**

 * struct clock_read_data - data required to read from sched_clock

 * 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

 * @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

 *			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
@@ -44,25 +45,26 @@ struct clock_read_data { 
};



/**

 * struct clock_data - all data needed for sched_clock (including

 * 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 clock read function

 * @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.

 * 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);

};
@@ -112,10 +114,10 @@ unsigned long long notrace sched_clock(void) 
/*

 * Updating the data required to read the clock.

 *

 * sched_clock will never observe mis-matched data even if called from

 * 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

 * 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.

 */
@@ -135,7 +137,7 @@ static void update_clock_read_data(struct clock_read_data *rd) 
}



/*

 * Atomically update the sched_clock epoch.

 * Atomically update the sched_clock() epoch.

 */

static void update_sched_clock(void)

{
@@ -146,9 +148,7 @@ static void update_sched_clock(void) 
	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);

	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;
@@ -160,11 +160,12 @@ 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)

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;
@@ -177,24 +178,22 @@ void __init sched_clock_register(u64 (*read)(void), int bits, 


	WARN_ON(!irqs_disabled());



	/* calculate the mult/shift to convert counter ticks to ns. */

	/* 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 */

	/* 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*/

	/* 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);

	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;
@@ -203,25 +202,29 @@ void __init sched_clock_register(u64 (*read)(void), int bits, 
	rd.shift		= new_shift;

	rd.epoch_cyc		= new_epoch;

	rd.epoch_ns		= ns;



	update_clock_read_data(&rd);



	r = rate;

	if (r >= 4000000) {

		r /= 1000000;

		r_unit = 'M';

	} else if (r >= 1000) {

	} else {

		if (r >= 1000) {

			r /= 1000;

			r_unit = 'k';

	} else

		} else {

			r_unit = ' ';

		}

	}



	/* calculate the ns resolution of this counter */

	/* 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 */

	/* Enable IRQ time accounting if we have a fast enough sched_clock() */

	if (irqtime > 0 || (irqtime == -1 && rate >= 1000000))

		enable_sched_clock_irqtime();
@@ -231,7 +234,7 @@ void __init sched_clock_register(u64 (*read)(void), int bits, 
void __init sched_clock_postinit(void)

{

	/*

	 * If no sched_clock function has been provided at that point,

	 * 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)
@@ -257,7 +260,7 @@ void __init sched_clock_postinit(void) 
 * 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.

 * correct copy of 'epoch_cyc'.

 */

static u64 notrace suspended_sched_clock_read(void)

{
@@ -273,6 +276,7 @@ static int sched_clock_suspend(void) 
	update_sched_clock();

	hrtimer_cancel(&sched_clock_timer);

	rd->read_sched_clock = suspended_sched_clock_read;



	return 0;

}
@@ -293,6 +297,7 @@ static struct syscore_ops sched_clock_ops = { 
static int __init sched_clock_syscore_init(void)

{

	register_syscore_ops(&sched_clock_ops);



	return 0;

}

device_initcall(sched_clock_syscore_init);

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