time: Refactor msecs_to_jiffies

Refactor the msecs_to_jiffies conditional code part in time.c and 
jiffies.h putting it into conditional functions rather than #ifdefs
to improve readability.

[ tglx: Verified that there is no binary code change ]

Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
Cc: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Joe Perches <joe@perches.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Andrew Hunter <ahh@google.com>
Cc: Paul Turner <pjt@google.com>
Cc: Michal Marek <mmarek@suse.cz>
Link: http://lkml.kernel.org/r/1431951554-5563-2-git-send-email-hofrat@osadl.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 19 insertions, 40 deletions

diff --git a/kernel/time/time.c b/kernel/time/time.c
index 4fa1d26a9843..c42c2c3214fe 100644
--- a/kernel/time/time.c
+++ b/kernel/time/time.c
@@ -483,9 +483,11 @@ struct timespec64 ns_to_timespec64(const s64 nsec)
 }
 EXPORT_SYMBOL(ns_to_timespec64);
 #endif
-/*
- * When we convert to jiffies then we interpret incoming values
- * the following way:
+/**
+ * msecs_to_jiffies: - convert milliseconds to jiffies
+ * @m:  time in milliseconds
+ *
+ * conversion is done as follows:
  *
  * - negative values mean 'infinite timeout' (MAX_JIFFY_OFFSET)
  *
@@ -493,51 +495,28 @@ EXPORT_SYMBOL(ns_to_timespec64);
  *   MAX_JIFFY_OFFSET values] mean 'infinite timeout' too.
  *
  * - all other values are converted to jiffies by either multiplying
- *   the input value by a factor or dividing it with a factor
- *
- * We must also be careful about 32-bit overflows.
+ *   the input value by a factor or dividing it with a factor and
+ *   handling any 32-bit overflows.
+ *   for the details see __msecs_to_jiffies()
+ *
+ * msecs_to_jiffies() checks for the passed in value being a constant
+ * via __builtin_constant_p() allowing gcc to eliminate most of the
+ * code, __msecs_to_jiffies() is called if the value passed does not
+ * allow constant folding and the actual conversion must be done at
+ * runtime.
+ * the _msecs_to_jiffies helpers are the HZ dependent conversion
+ * routines found in include/linux/jiffies.h
  */
-unsigned long msecs_to_jiffies(const unsigned int m)
+unsigned long __msecs_to_jiffies(const unsigned int m)
 {
         /*
          * Negative value, means infinite timeout:
          */
         if ((int)m < 0)
                 return MAX_JIFFY_OFFSET;
-
-#if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
-        /*
-         * HZ is equal to or smaller than 1000, and 1000 is a nice
-         * round multiple of HZ, divide with the factor between them,
-         * but round upwards:
-         */
-        return (m + (MSEC_PER_SEC / HZ) - 1) / (MSEC_PER_SEC / HZ);
-#elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
-        /*
-         * HZ is larger than 1000, and HZ is a nice round multiple of
-         * 1000 - simply multiply with the factor between them.
-         *
-         * But first make sure the multiplication result cannot
-         * overflow:
-         */
-        if (m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
-                return MAX_JIFFY_OFFSET;
-
-        return m * (HZ / MSEC_PER_SEC);
-#else
-        /*
-         * Generic case - multiply, round and divide. But first
-         * check that if we are doing a net multiplication, that
-         * we wouldn't overflow:
-         */
-        if (HZ > MSEC_PER_SEC && m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
-                return MAX_JIFFY_OFFSET;
-
-        return (MSEC_TO_HZ_MUL32 * m + MSEC_TO_HZ_ADJ32)
-                >> MSEC_TO_HZ_SHR32;
-#endif
+        return _msecs_to_jiffies(m);
 }
-EXPORT_SYMBOL(msecs_to_jiffies);
+EXPORT_SYMBOL(__msecs_to_jiffies);
 
 unsigned long usecs_to_jiffies(const unsigned int u)
 {