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authorjohn stultz <johnstul@us.ibm.com>2007-07-24 18:38:34 -0700
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-07-25 10:17:44 -0700
commit17c38b7490b3f0300c7812aefdae2ddda7ab4112 (patch)
tree0f7a9ee0c691aef3497030e38c3ba8e3c13a985c /kernel
parent2c6b47de17c75d553de3e2fb426d8298d2074585 (diff)
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Cache xtime every call to update_wall_time
This avoids xtime lag seen with dynticks, because while 'xtime' itself is still not updated often, we keep a 'xtime_cache' variable around that contains the approximate real-time that _is_ updated each time we do a 'update_wall_time()', and is thus never off by more than one tick. IOW, this restores the original semantics for 'xtime' users, as long as you use the proper abstraction functions (ie 'current_kernel_time()' or 'get_seconds()' depending on whether you want a timespec or just the seconds field). [ Updated Patch. As penance for my sins I've also yanked another #ifdef that was added to avoid the xtime lag w/ hrtimers. ] Signed-off-by: John Stultz <johnstul@us.ibm.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/hrtimer.c4
-rw-r--r--kernel/time/timekeeping.c26
2 files changed, 23 insertions, 7 deletions
diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index a7bb05e6cb6..c21ca6bfaa6 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -141,11 +141,7 @@ static void hrtimer_get_softirq_time(struct hrtimer_cpu_base *base)
do {
seq = read_seqbegin(&xtime_lock);
-#ifdef CONFIG_NO_HZ
- getnstimeofday(&xts);
-#else
xts = current_kernel_time();
-#endif
tom = wall_to_monotonic;
} while (read_seqretry(&xtime_lock, seq));
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 07a3f1420c2..acc417b5a9b 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -47,10 +47,22 @@ EXPORT_SYMBOL(xtime_lock);
struct timespec xtime __attribute__ ((aligned (16)));
struct timespec wall_to_monotonic __attribute__ ((aligned (16)));
static unsigned long total_sleep_time; /* seconds */
-
EXPORT_SYMBOL(xtime);
+#ifdef CONFIG_NO_HZ
+static struct timespec xtime_cache __attribute__ ((aligned (16)));
+static inline void update_xtime_cache(u64 nsec)
+{
+ xtime_cache = xtime;
+ timespec_add_ns(&xtime_cache, nsec);
+}
+#else
+#define xtime_cache xtime
+/* We do *not* want to evaluate the argument for this case */
+#define update_xtime_cache(n) do { } while (0)
+#endif
+
static struct clocksource *clock; /* pointer to current clocksource */
@@ -478,6 +490,8 @@ void update_wall_time(void)
xtime.tv_nsec = (s64)clock->xtime_nsec >> clock->shift;
clock->xtime_nsec -= (s64)xtime.tv_nsec << clock->shift;
+ update_xtime_cache(cyc2ns(clock, offset));
+
/* check to see if there is a new clocksource to use */
change_clocksource();
update_vsyscall(&xtime, clock);
@@ -510,6 +524,13 @@ void monotonic_to_bootbased(struct timespec *ts)
ts->tv_sec += total_sleep_time;
}
+unsigned long get_seconds(void)
+{
+ return xtime_cache.tv_sec;
+}
+EXPORT_SYMBOL(get_seconds);
+
+
struct timespec current_kernel_time(void)
{
struct timespec now;
@@ -518,10 +539,9 @@ struct timespec current_kernel_time(void)
do {
seq = read_seqbegin(&xtime_lock);
- now = xtime;
+ now = xtime_cache;
} while (read_seqretry(&xtime_lock, seq));
return now;
}
-
EXPORT_SYMBOL(current_kernel_time);