hrtimers: Reorder clock bases

The ordering of the clock bases is historical due to the
CLOCK_REALTIME and CLOCK_MONOTONIC constants. Now the hrtimer bases
have their own enumeration due to the gap between CLOCK_MONOTONIC and
CLOCK_BOOTTIME. So we can be more clever as most timers end up on the
CLOCK_MONOTONIC base due to the virtue of POSIX declaring that
relative CLOCK_REALTIME timers are not affected by time changes. In
desktop environments this is slowly changing as applications switch to
absolute timers, but I've observed empty CLOCK_REALTIME bases often
enough. There is no performance penalty or overhead when
CLOCK_REALTIME timers are active, but in case they are not we don't
skip over a full cache line.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Peter Zijlstra <peterz@infradead.org>

2 files changed, 7 insertions, 7 deletions

diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
index 771c95802edc..51932e5acf7c 100644
--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -153,8 +153,8 @@ struct hrtimer_clock_base {
 };
 
 enum  hrtimer_base_type {
-        HRTIMER_BASE_REALTIME,
         HRTIMER_BASE_MONOTONIC,
+        HRTIMER_BASE_REALTIME,
         HRTIMER_BASE_BOOTTIME,
         HRTIMER_MAX_CLOCK_BASES,
 };
diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index 1b08f6d67f12..c541ee527ecb 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -64,18 +64,18 @@ DEFINE_PER_CPU(struct hrtimer_cpu_base, hrtimer_bases) =
         .clock_base =
         {
                 {
-                        .index = HRTIMER_BASE_REALTIME,
-                        .clockid = CLOCK_REALTIME,
-                        .get_time = &ktime_get_real,
-                        .resolution = KTIME_LOW_RES,
-                },
-                {
                         .index = HRTIMER_BASE_MONOTONIC,
                         .clockid = CLOCK_MONOTONIC,
                         .get_time = &ktime_get,
                         .resolution = KTIME_LOW_RES,
                 },
                 {
+                        .index = HRTIMER_BASE_REALTIME,
+                        .clockid = CLOCK_REALTIME,
+                        .get_time = &ktime_get_real,
+                        .resolution = KTIME_LOW_RES,
+                },
+                {
                         .index = HRTIMER_BASE_BOOTTIME,
                         .clockid = CLOCK_BOOTTIME,
                         .get_time = &ktime_get_boottime,