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

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.comSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent ed5c8c85
...@@ -27,19 +27,8 @@ ...@@ -27,19 +27,8 @@
#include "timekeeping.h" #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 * conversion, the .shift value could be zero. However
* this would make NTP adjustments impossible as they are * this would make NTP adjustments impossible as they are
* in units of 1/2^.shift. Thus we use JIFFIES_SHIFT to * in units of 1/2^.shift. Thus we use JIFFIES_SHIFT to
...@@ -47,8 +36,8 @@ ...@@ -47,8 +36,8 @@
* amount, and give ntp adjustments in units of 1/2^8 * amount, and give ntp adjustments in units of 1/2^8
* *
* The value 8 is somewhat carefully chosen, as anything * The value 8 is somewhat carefully chosen, as anything
* larger can result in overflows. NSEC_PER_JIFFY grows as * larger can result in overflows. TICK_NSEC grows as HZ
* HZ shrinks, so values greater than 8 overflow 32bits when * shrinks, so values greater than 8 overflow 32bits when
* HZ=100. * HZ=100.
*/ */
#if HZ < 34 #if HZ < 34
...@@ -64,12 +53,23 @@ static u64 jiffies_read(struct clocksource *cs) ...@@ -64,12 +53,23 @@ static u64 jiffies_read(struct clocksource *cs)
return (u64) jiffies; 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 = { static struct clocksource clocksource_jiffies = {
.name = "jiffies", .name = "jiffies",
.rating = 1, /* lowest valid rating*/ .rating = 1, /* lowest valid rating*/
.read = jiffies_read, .read = jiffies_read,
.mask = CLOCKSOURCE_MASK(32), .mask = CLOCKSOURCE_MASK(32),
.mult = NSEC_PER_JIFFY << JIFFIES_SHIFT, /* details above */ .mult = TICK_NSEC << JIFFIES_SHIFT, /* details above */
.shift = JIFFIES_SHIFT, .shift = JIFFIES_SHIFT,
.max_cycles = 10, .max_cycles = 10,
}; };
...@@ -125,7 +125,7 @@ int register_refined_jiffies(long cycles_per_second) ...@@ -125,7 +125,7 @@ int register_refined_jiffies(long cycles_per_second)
shift_hz += cycles_per_tick/2; shift_hz += cycles_per_tick/2;
do_div(shift_hz, cycles_per_tick); do_div(shift_hz, cycles_per_tick);
/* Calculate nsec_per_tick using shift_hz */ /* 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; nsec_per_tick += (u32)shift_hz/2;
do_div(nsec_per_tick, (u32)shift_hz); do_div(nsec_per_tick, (u32)shift_hz);
......
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