[PATCH] hrtimer: introduce ktime_t time format

- introduce ktime_t: nanosecond-resolution time format.

- eliminate the plain s64 scalar type, and always use the union.
  This simplifies the arithmetics. Idea from Roman Zippel.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 273 insertions, 0 deletions

diff --git a/arch/i386/Kconfig b/arch/i386/Kconfig
index 554ce3f344c9..815878ebd30f 100644
--- a/arch/i386/Kconfig
+++ b/arch/i386/Kconfig
@@ -1060,3 +1060,7 @@ config X86_TRAMPOLINE
         bool
         depends on X86_SMP || (X86_VOYAGER && SMP)
         default y
+
+config KTIME_SCALAR
+        bool
+        default y
diff --git a/include/linux/ktime.h b/include/linux/ktime.h
new file mode 100644
index 000000000000..5b9a9eb82baa
--- /dev/null
+++ b/include/linux/ktime.h
@@ -0,0 +1,269 @@
+/*
+ *  include/linux/ktime.h
+ *
+ *  ktime_t - nanosecond-resolution time format.
+ *
+ *   Copyright(C) 2005, Thomas Gleixner <tglx@linutronix.de>
+ *   Copyright(C) 2005, Red Hat, Inc., Ingo Molnar
+ *
+ *  data type definitions, declarations, prototypes and macros.
+ *
+ *  Started by: Thomas Gleixner and Ingo Molnar
+ *
+ *  For licencing details see kernel-base/COPYING
+ */
+#ifndef _LINUX_KTIME_H
+#define _LINUX_KTIME_H
+
+#include <linux/time.h>
+#include <linux/jiffies.h>
+
+/*
+ * ktime_t:
+ *
+ * On 64-bit CPUs a single 64-bit variable is used to store the hrtimers
+ * internal representation of time values in scalar nanoseconds. The
+ * design plays out best on 64-bit CPUs, where most conversions are
+ * NOPs and most arithmetic ktime_t operations are plain arithmetic
+ * operations.
+ *
+ * On 32-bit CPUs an optimized representation of the timespec structure
+ * is used to avoid expensive conversions from and to timespecs. The
+ * endian-aware order of the tv struct members is choosen to allow
+ * mathematical operations on the tv64 member of the union too, which
+ * for certain operations produces better code.
+ *
+ * For architectures with efficient support for 64/32-bit conversions the
+ * plain scalar nanosecond based representation can be selected by the
+ * config switch CONFIG_KTIME_SCALAR.
+ */
+typedef union {
+        s64     tv64;
+#if BITS_PER_LONG != 64 && !defined(CONFIG_KTIME_SCALAR)
+        struct {
+# ifdef __BIG_ENDIAN
+        s32     sec, nsec;
+# else
+        s32     nsec, sec;
+# endif
+        } tv;
+#endif
+} ktime_t;
+
+#define KTIME_MAX                       (~((u64)1 << 63))
+
+/*
+ * ktime_t definitions when using the 64-bit scalar representation:
+ */
+
+#if (BITS_PER_LONG == 64) || defined(CONFIG_KTIME_SCALAR)
+
+/* Define a ktime_t variable and initialize it to zero: */
+#define DEFINE_KTIME(kt)                ktime_t kt = { .tv64 = 0 }
+
+/**
+ * ktime_set - Set a ktime_t variable from a seconds/nanoseconds value
+ *
+ * @secs:       seconds to set
+ * @nsecs:      nanoseconds to set
+ *
+ * Return the ktime_t representation of the value
+ */
+static inline ktime_t ktime_set(const long secs, const unsigned long nsecs)
+{
+        return (ktime_t) { .tv64 = (s64)secs * NSEC_PER_SEC + (s64)nsecs };
+}
+
+/* Subtract two ktime_t variables. rem = lhs -rhs: */
+#define ktime_sub(lhs, rhs) \
+                ({ (ktime_t){ .tv64 = (lhs).tv64 - (rhs).tv64 }; })
+
+/* Add two ktime_t variables. res = lhs + rhs: */
+#define ktime_add(lhs, rhs) \
+                ({ (ktime_t){ .tv64 = (lhs).tv64 + (rhs).tv64 }; })
+
+/*
+ * Add a ktime_t variable and a scalar nanosecond value.
+ * res = kt + nsval:
+ */
+#define ktime_add_ns(kt, nsval) \
+                ({ (ktime_t){ .tv64 = (kt).tv64 + (nsval) }; })
+
+/* convert a timespec to ktime_t format: */
+#define timespec_to_ktime(ts)           ktime_set((ts).tv_sec, (ts).tv_nsec)
+
+/* convert a timeval to ktime_t format: */
+#define timeval_to_ktime(tv)            ktime_set((tv).tv_sec, (tv).tv_usec * 1000)
+
+/* Map the ktime_t to timespec conversion to ns_to_timespec function */
+#define ktime_to_timespec(kt)           ns_to_timespec((kt).tv64)
+
+/* Map the ktime_t to timeval conversion to ns_to_timeval function */
+#define ktime_to_timeval(kt)            ns_to_timeval((kt).tv64)
+
+/* Map the ktime_t to clock_t conversion to the inline in jiffies.h: */
+#define ktime_to_clock_t(kt)            nsec_to_clock_t((kt).tv64)
+
+/* Convert ktime_t to nanoseconds - NOP in the scalar storage format: */
+#define ktime_to_ns(kt)                 ((kt).tv64)
+
+#else
+
+/*
+ * Helper macros/inlines to get the ktime_t math right in the timespec
+ * representation. The macros are sometimes ugly - their actual use is
+ * pretty okay-ish, given the circumstances. We do all this for
+ * performance reasons. The pure scalar nsec_t based code was nice and
+ * simple, but created too many 64-bit / 32-bit conversions and divisions.
+ *
+ * Be especially aware that negative values are represented in a way
+ * that the tv.sec field is negative and the tv.nsec field is greater
+ * or equal to zero but less than nanoseconds per second. This is the
+ * same representation which is used by timespecs.
+ *
+ *   tv.sec < 0 and 0 >= tv.nsec < NSEC_PER_SEC
+ */
+
+/* Define a ktime_t variable and initialize it to zero: */
+#define DEFINE_KTIME(kt)                ktime_t kt = { .tv64 = 0 }
+
+/* Set a ktime_t variable to a value in sec/nsec representation: */
+static inline ktime_t ktime_set(const long secs, const unsigned long nsecs)
+{
+        return (ktime_t) { .tv = { .sec = secs, .nsec = nsecs } };
+}
+
+/**
+ * ktime_sub - subtract two ktime_t variables
+ *
+ * @lhs:        minuend
+ * @rhs:        subtrahend
+ *
+ * Returns the remainder of the substraction
+ */
+static inline ktime_t ktime_sub(const ktime_t lhs, const ktime_t rhs)
+{
+        ktime_t res;
+
+        res.tv64 = lhs.tv64 - rhs.tv64;
+        if (res.tv.nsec < 0)
+                res.tv.nsec += NSEC_PER_SEC;
+
+        return res;
+}
+
+/**
+ * ktime_add - add two ktime_t variables
+ *
+ * @add1:       addend1
+ * @add2:       addend2
+ *
+ * Returns the sum of addend1 and addend2
+ */
+static inline ktime_t ktime_add(const ktime_t add1, const ktime_t add2)
+{
+        ktime_t res;
+
+        res.tv64 = add1.tv64 + add2.tv64;
+        /*
+         * performance trick: the (u32) -NSEC gives 0x00000000Fxxxxxxx
+         * so we subtract NSEC_PER_SEC and add 1 to the upper 32 bit.
+         *
+         * it's equivalent to:
+         *   tv.nsec -= NSEC_PER_SEC
+         *   tv.sec ++;
+         */
+        if (res.tv.nsec >= NSEC_PER_SEC)
+                res.tv64 += (u32)-NSEC_PER_SEC;
+
+        return res;
+}
+
+/**
+ * ktime_add_ns - Add a scalar nanoseconds value to a ktime_t variable
+ *
+ * @kt:         addend
+ * @nsec:       the scalar nsec value to add
+ *
+ * Returns the sum of kt and nsec in ktime_t format
+ */
+extern ktime_t ktime_add_ns(const ktime_t kt, u64 nsec);
+
+/**
+ * timespec_to_ktime - convert a timespec to ktime_t format
+ *
+ * @ts:         the timespec variable to convert
+ *
+ * Returns a ktime_t variable with the converted timespec value
+ */
+static inline ktime_t timespec_to_ktime(const struct timespec ts)
+{
+        return (ktime_t) { .tv = { .sec = (s32)ts.tv_sec,
+                                   .nsec = (s32)ts.tv_nsec } };
+}
+
+/**
+ * timeval_to_ktime - convert a timeval to ktime_t format
+ *
+ * @tv:         the timeval variable to convert
+ *
+ * Returns a ktime_t variable with the converted timeval value
+ */
+static inline ktime_t timeval_to_ktime(const struct timeval tv)
+{
+        return (ktime_t) { .tv = { .sec = (s32)tv.tv_sec,
+                                   .nsec = (s32)tv.tv_usec * 1000 } };
+}
+
+/**
+ * ktime_to_timespec - convert a ktime_t variable to timespec format
+ *
+ * @kt:         the ktime_t variable to convert
+ *
+ * Returns the timespec representation of the ktime value
+ */
+static inline struct timespec ktime_to_timespec(const ktime_t kt)
+{
+        return (struct timespec) { .tv_sec = (time_t) kt.tv.sec,
+                                   .tv_nsec = (long) kt.tv.nsec };
+}
+
+/**
+ * ktime_to_timeval - convert a ktime_t variable to timeval format
+ *
+ * @kt:         the ktime_t variable to convert
+ *
+ * Returns the timeval representation of the ktime value
+ */
+static inline struct timeval ktime_to_timeval(const ktime_t kt)
+{
+        return (struct timeval) {
+                .tv_sec = (time_t) kt.tv.sec,
+                .tv_usec = (suseconds_t) (kt.tv.nsec / NSEC_PER_USEC) };
+}
+
+/**
+ * ktime_to_clock_t - convert a ktime_t variable to clock_t format
+ * @kt:         the ktime_t variable to convert
+ *
+ * Returns a clock_t variable with the converted value
+ */
+static inline clock_t ktime_to_clock_t(const ktime_t kt)
+{
+        return nsec_to_clock_t( (u64) kt.tv.sec * NSEC_PER_SEC + kt.tv.nsec);
+}
+
+/**
+ * ktime_to_ns - convert a ktime_t variable to scalar nanoseconds
+ * @kt:         the ktime_t variable to convert
+ *
+ * Returns the scalar nanoseconds representation of kt
+ */
+static inline u64 ktime_to_ns(const ktime_t kt)
+{
+        return (u64) kt.tv.sec * NSEC_PER_SEC + kt.tv.nsec;
+}
+
+#endif
+
+#endif