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authorThomas Gleixner <tglx@linutronix.de>2017-08-31 18:12:48 +0300
committerThomas Gleixner <tglx@linutronix.de>2017-09-25 22:05:59 +0300
commit4c3711d7fb4763c63b2654f2d07cbe21ca5aadd4 (patch)
tree8601fdab0f9b823f687d0ae5ddef6b7ef6046710 /include/linux/timekeeping.h
parent5df32107f609c1f621bcdac0a685c23677ef671e (diff)
downloadlinux-4c3711d7fb4763c63b2654f2d07cbe21ca5aadd4.tar.xz
timekeeping: Provide NMI safe access to clock realtime
The configurable printk timestamping wants access to clock realtime. Right now there is no ktime_get_real_fast_ns() accessor because reading the monotonic base and the realtime offset cannot be done atomically. Contrary to boot time this offset can change during runtime and cause half updated readouts. struct tk_read_base was fully packed when the fast timekeeper access was implemented. commit ceea5e3771ed ("time: Fix clock->read(clock) race around clocksource changes") removed the 'read' function pointer from the structure, but of course left the comment stale. So now the structure can fit a new 64bit member w/o violating the cache line constraints. Add real_base to tk_read_base and update it in the fast timekeeper update sequence. Implement an accessor which follows the same scheme as the accessor to clock monotonic, but uses the new real_base to access clock real time. The runtime overhead for updating real_base is minimal as it just adds two cache hot values and stores them into an already dirtied cache line along with the other fast timekeeper updates. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Prarit Bhargava <prarit@redhat.com> Cc: John Stultz <john.stultz@linaro.org> Cc: Peter Zijlstra <peterz@infradead,org> Link: https://lkml.kernel.org/r/1505757060-2004-3-git-send-email-prarit@redhat.com
Diffstat (limited to 'include/linux/timekeeping.h')
-rw-r--r--include/linux/timekeeping.h1
1 files changed, 1 insertions, 0 deletions
diff --git a/include/linux/timekeeping.h b/include/linux/timekeeping.h
index ddc229ff6d1e..eb98cbdbb323 100644
--- a/include/linux/timekeeping.h
+++ b/include/linux/timekeeping.h
@@ -239,6 +239,7 @@ static inline u64 ktime_get_raw_ns(void)
extern u64 ktime_get_mono_fast_ns(void);
extern u64 ktime_get_raw_fast_ns(void);
extern u64 ktime_get_boot_fast_ns(void);
+extern u64 ktime_get_real_fast_ns(void);
/*
* Timespec interfaces utilizing the ktime based ones