Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 93825f2e authored by Frederic Weisbecker's avatar Frederic Weisbecker Committed by Ingo Molnar
Browse files

jiffies: Reuse TICK_NSEC instead of NSEC_PER_JIFFY 



NSEC_PER_JIFFY is an ad-hoc redefinition of TICK_NSEC. Let's rather
use a unique and well maintained version.

Signed-off-by: default avatarFrederic Weisbecker <fweisbec@gmail.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Stanislaw Gruszka <sgruszka@redhat.com>
Cc: Wanpeng Li <wanpeng.li@hotmail.com>
Link: http://lkml.kernel.org/r/1485832191-26889-1-git-send-email-fweisbec@gmail.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent ed5c8c85

kernel/time/jiffies.c

+16 −16
Original line number Diff line number Diff line
@@ -27,19 +27,8 @@ 


#include "timekeeping.h"



/* The Jiffies based clocksource is the lowest common

 * denominator clock source which should function on

 * all systems. It has the same coarse resolution as

 * the timer interrupt frequency HZ and it suffers

 * inaccuracies caused by missed or lost timer

 * interrupts and the inability for the timer

 * interrupt hardware to accuratly tick at the

 * requested HZ value. It is also not recommended

 * for "tick-less" systems.

 */

#define NSEC_PER_JIFFY	((NSEC_PER_SEC+HZ/2)/HZ)



/* Since jiffies uses a simple NSEC_PER_JIFFY multiplier

/* Since jiffies uses a simple TICK_NSEC multiplier

 * conversion, the .shift value could be zero. However

 * this would make NTP adjustments impossible as they are

 * in units of 1/2^.shift. Thus we use JIFFIES_SHIFT to
@@ -47,8 +36,8 @@ 
 * amount, and give ntp adjustments in units of 1/2^8

 *

 * The value 8 is somewhat carefully chosen, as anything

 * larger can result in overflows. NSEC_PER_JIFFY grows as

 * HZ shrinks, so values greater than 8 overflow 32bits when

 * larger can result in overflows. TICK_NSEC grows as HZ

 * shrinks, so values greater than 8 overflow 32bits when

 * HZ=100.

 */

#if HZ < 34
@@ -64,12 +53,23 @@ static u64 jiffies_read(struct clocksource *cs) 
	return (u64) jiffies;

}



/*

 * The Jiffies based clocksource is the lowest common

 * denominator clock source which should function on

 * all systems. It has the same coarse resolution as

 * the timer interrupt frequency HZ and it suffers

 * inaccuracies caused by missed or lost timer

 * interrupts and the inability for the timer

 * interrupt hardware to accuratly tick at the

 * requested HZ value. It is also not recommended

 * for "tick-less" systems.

 */

static struct clocksource clocksource_jiffies = {

	.name		= "jiffies",

	.rating		= 1, /* lowest valid rating*/

	.read		= jiffies_read,

	.mask		= CLOCKSOURCE_MASK(32),

	.mult		= NSEC_PER_JIFFY << JIFFIES_SHIFT, /* details above */

	.mult		= TICK_NSEC << JIFFIES_SHIFT, /* details above */

	.shift		= JIFFIES_SHIFT,

	.max_cycles	= 10,

};
@@ -125,7 +125,7 @@ int register_refined_jiffies(long cycles_per_second) 
	shift_hz += cycles_per_tick/2;

	do_div(shift_hz, cycles_per_tick);

	/* Calculate nsec_per_tick using shift_hz */

	nsec_per_tick = (u64)NSEC_PER_SEC << 8;

	nsec_per_tick = (u64)TICK_NSEC << 8;

	nsec_per_tick += (u32)shift_hz/2;

	do_div(nsec_per_tick, (u32)shift_hz);