timekeeping: Provide hrtimer update function

commit f6c06abfb3972ad4914cef57d8348fcb2932bc3b upstream.

To finally fix the infamous leap second issue and other race windows
caused by functions which change the offsets between the various time
bases (CLOCK_MONOTONIC, CLOCK_REALTIME and CLOCK_BOOTTIME) we need a
function which atomically gets the current monotonic time and updates
the offsets of CLOCK_REALTIME and CLOCK_BOOTTIME with minimalistic
overhead. The previous patch which provides ktime_t offsets allows us
to make this function almost as cheap as ktime_get() which is going to
be replaced in hrtimer_interrupt().

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Prarit Bhargava <prarit@redhat.com>
Signed-off-by: John Stultz <johnstul@us.ibm.com>
Link: http://lkml.kernel.org/r/1341960205-56738-7-git-send-email-johnstul@us.ibm.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Linux Kernel <linux-kernel@vger.kernel.org>
Signed-off-by: John Stultz <johnstul@us.ibm.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
index 0325598fc700fa0cef84740ca3b82eb94ce55abc..887d1e73c4daf5a0c1438f66bcd39b441bfd003b 100644 (file)
--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -319,7 +319,7 @@ static inline void clock_was_set_delayed(void) { }
 
 extern ktime_t ktime_get(void);
 extern ktime_t ktime_get_real(void);
-
+extern ktime_t ktime_get_update_offsets(ktime_t *offs_real);
 
 DECLARE_PER_CPU(struct tick_device, tick_cpu_device);
 

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 3d443b4e7aa4d94846d5c5e78c06ac9aaf7af85a..0b4f6d1c282bdc309f9d2ad8c3600903bcb6a54f 100644 (file)
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -969,3 +969,35 @@ struct timespec get_monotonic_coarse(void)
                                now.tv_nsec + mono.tv_nsec);
        return now;
 }
+
+#ifdef CONFIG_HIGH_RES_TIMERS
+/**
+ * ktime_get_update_offsets - hrtimer helper
+ * @real:      pointer to storage for monotonic -> realtime offset
+ *
+ * Returns current monotonic time and updates the offsets
+ * Called from hrtimer_interupt() or retrigger_next_event()
+ */
+ktime_t ktime_get_update_offsets(ktime_t *real)
+{
+       ktime_t now;
+       unsigned int seq;
+       u64 secs, nsecs;
+
+       do {
+               seq = read_seqbegin(&xtime_lock);
+
+               secs = xtime.tv_sec;
+               nsecs = xtime.tv_nsec;
+               nsecs += timekeeping_get_ns();
+               /* If arch requires, add in gettimeoffset() */
+               nsecs += arch_gettimeoffset();
+
+               *real = offs_real;
+       } while (read_seqretry(&xtime_lock, seq));
+
+       now = ktime_add_ns(ktime_set(secs, 0), nsecs);
+       now = ktime_sub(now, *real);
+       return now;
+}
+#endif