[PATCH RESEND 01/36] jiffies: Reuse TICK_NSEC instead of NSEC_PER_JIFFY

Frederic Weisbecker
2017-01-31T03:18:59Z

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

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: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Stanislaw Gruszka <sgruszka@redhat.com>
Cc: Wanpeng Li <wanpeng.li@hotmail.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
---
kernel/time/jiffies.c | 32 ++++++++++++++++----------------
1 file changed, 16 insertions(+), 16 deletions(-)

diff --git a/kernel/time/jiffies.c b/kernel/time/jiffies.c
index a4a0e47..7906b3f 100644
--- a/kernel/time/jiffies.c
+++ b/kernel/time/jiffies.c
@@ -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);

--
2.7.4