linux-kernel - [RFC v8 20/28] clockevents: degrade ->min_delta

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Date:   Sat, 19 Nov 2016 17:10:28 +0100
From:   Nicolai Stange <nicstange@...il.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     John Stultz <john.stultz@...aro.org>, linux-kernel@...r.kernel.org,
        Nicolai Stange <nicstange@...il.com>
Subject: [RFC v8 20/28] clockevents: degrade ->min_delta_ticks to unsigned int

While being of type unsigned long right now, the ->min_delta_ticks and
->min_delta_ticks_adjusted members of struct clock_event_device aren't
expected to ever overflow an unsigned int.

The latter sits in the first cacheline. For the case of
sizeof(long) > sizeof(int), this is a waste of precious space needed by
later patches.

Degrade the types of ->min_delta_ticks_adjusted and ->min_delta_ticks
from unsigned long to unsigned int.
Change casts in the clockevents core were needed.
Adapt the signature of clockevents_config_and_register() accordingly.
Finally, move ->min_delta_ticks farther down the struct in order to
allow for alignment with other ints, potentially avoiding padding.

Signed-off-by: Nicolai Stange <nicstange@...il.com>
---
 include/linux/clockchips.h | 8 ++++----
 kernel/time/clockevents.c  | 6 +++---
 2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/include/linux/clockchips.h b/include/linux/clockchips.h
index 76fc51b..c8dfc7a 100644
--- a/include/linux/clockchips.h
+++ b/include/linux/clockchips.h
@@ -92,9 +92,9 @@ enum clock_event_state {
  * @set_state_shutdown:	switch state to shutdown
  * @tick_resume:	resume clkevt device
  * @broadcast:		function to broadcast events
- * @min_delta_ticks:	minimum delta value in ticks stored for reconfiguration
  * @max_delta_ticks:	maximum delta value in ticks stored for reconfiguration
  * @name:		ptr to clock event name
+ * @min_delta_ticks:	minimum delta value in ticks stored for reconfiguration
  * @rating:		variable to rate clock event devices
  * @irq:		IRQ number (only for non CPU local devices)
  * @bound_on:		Bound on CPU
@@ -108,7 +108,7 @@ struct clock_event_device {
 	int			(*set_next_ktime)(ktime_t expires, struct clock_event_device *);
 	ktime_t			next_event;
 	u64			max_delta_ns;
-	unsigned long		min_delta_ticks_adjusted;
+	unsigned int		min_delta_ticks_adjusted;
 	u32			mult;
 	u32			shift;
 	enum clock_event_state	state_use_accessors;
@@ -124,10 +124,10 @@ struct clock_event_device {
 	void			(*broadcast)(const struct cpumask *mask);
 	void			(*suspend)(struct clock_event_device *);
 	void			(*resume)(struct clock_event_device *);
-	unsigned long		min_delta_ticks;
 	unsigned long		max_delta_ticks;
 
 	const char		*name;
+	unsigned int		min_delta_ticks;
 	int			rating;
 	int			irq;
 	int			bound_on;
@@ -189,7 +189,7 @@ extern void clockevents_register_device(struct clock_event_device *dev);
 extern int clockevents_unbind_device(struct clock_event_device *ced, int cpu);
 
 extern void clockevents_config_and_register(struct clock_event_device *dev,
-					    u32 freq, unsigned long min_delta,
+					    u32 freq, unsigned int min_delta,
 					    unsigned long max_delta);
 
 extern int clockevents_update_freq(struct clock_event_device *ce, u32 freq);
diff --git a/kernel/time/clockevents.c b/kernel/time/clockevents.c
index 57b00b0..84639a1 100644
--- a/kernel/time/clockevents.c
+++ b/kernel/time/clockevents.c
@@ -228,7 +228,7 @@ static int clockevents_increase_min_delta(struct clock_event_device *dev)
 	if (min_delta_ns > MIN_DELTA_LIMIT)
 		min_delta_ns = MIN_DELTA_LIMIT;
 
-	dev->min_delta_ticks_adjusted = (unsigned long)((min_delta_ns *
+	dev->min_delta_ticks_adjusted = (unsigned int)((min_delta_ns *
 						dev->mult) >> dev->shift);
 
 	printk_deferred(KERN_WARNING
@@ -451,7 +451,7 @@ static void __clockevents_update_bounds(struct clock_event_device *dev)
 	 */
 	dev->min_delta_ticks_adjusted =
 		max(dev->min_delta_ticks,
-			(unsigned long)((1000ULL * dev->mult) >> dev->shift));
+			(unsigned int)((1000ULL * dev->mult) >> dev->shift));
 }
 
 /**
@@ -514,7 +514,7 @@ static void clockevents_config(struct clock_event_device *dev, u32 freq)
  * min/max_delta can be 0 for devices which do not support oneshot mode.
  */
 void clockevents_config_and_register(struct clock_event_device *dev,
-				     u32 freq, unsigned long min_delta,
+				     u32 freq, unsigned int min_delta,
 				     unsigned long max_delta)
 {
 	dev->min_delta_ticks = min_delta;
-- 
2.10.2