[PATCH v6 3/9] Add correlated clocksource relating aliased auxiliary and system clocks
From: Christopher S. Hall
Date: Wed Jan 13 2016 - 14:22:22 EST
ACKNOWLEDGMENT: The original correlated clock source and cross
timestamp code was developed by Thomas Gleixner
<tglx@xxxxxxxxxxxxx>. It has changed considerably and any mistakes are
mine.
The timekeeping and clocksource code don't currently comprehend two
clocks that are aliases of one another. That is clocks that are
*exactly* related. The correlated_cs struct encapsulated this
relationship between a clocksource and its alias clock. Modern Intel
hardware provides an Always Running Timer (ART) which is exactly
related to TSC through a known frequency ratio. The ART is an example
of a correlated clocksource.
Signed-off-by: Christopher S. Hall <christopher.s.hall@xxxxxxxxx>
---
include/linux/clocksource.h | 14 ++++++++++++++
1 file changed, 14 insertions(+)
diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
index 4542293..726ca68 100644
--- a/include/linux/clocksource.h
+++ b/include/linux/clocksource.h
@@ -267,4 +267,18 @@ struct system_counterval_t {
struct clocksource *cs;
};
+/*
+ * struct correlated_cs - Descriptor for a clocksource correlated to another
+ * clocksource
+ * @related_cs: Pointer to the related timekeeping clocksource
+ * @convert: Conversion function to convert a timestamp from
+ * the correlated clocksource to cycles of the related
+ * timekeeping clocksource
+ */
+struct correlated_cs {
+ struct clocksource *related_cs;
+ cycle_t (*convert)(struct correlated_cs *cs,
+ cycle_t cycles);
+};
+
#endif /* _LINUX_CLOCKSOURCE_H */
--
2.1.4