[PATCH] jiffies conversions: Use compile time constants when possible

Joe Perches
2013-01-04T21:15:44Z

Do the multiplications and divisions at compile time
instead of runtime when the converted value is a constant.

Make the calculation functions static __always_inline to jiffies.h.

Add #defines with __builtin_constant_p to test and use the
static inline or the runtime functions as appropriate.

Prefix the old exported symbols/functions with __

Signed-off-by: Joe Perches <joe@perches.com>
---
include/linux/jiffies.h | 136 ++++++++++++++++++++++++++++++++++++++++++++++--
kernel/time.c | 106 +++++--------------------------------
2 files changed, 144 insertions(+), 98 deletions(-)

diff --git a/include/linux/jiffies.h b/include/linux/jiffies.h
index 82ed068..88578e4 100644
--- a/include/linux/jiffies.h
+++ b/include/linux/jiffies.h
@@ -289,10 +289,138 @@ extern unsigned long preset_lpj;
/*
* Convert various time units to each other:
*/
-extern unsigned int jiffies_to_msecs(const unsigned long j);
-extern unsigned int jiffies_to_usecs(const unsigned long j);
-extern unsigned long msecs_to_jiffies(const unsigned int m);
-extern unsigned long usecs_to_jiffies(const unsigned int u);
+
+/*
+ * Avoid unnecessary multiplications/divisions in the
+ * two most common HZ cases:
+ */
+static __always_inline unsigned int
+__inline_jiffies_to_msecs(const unsigned long j)
+{
+#if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
+ return (MSEC_PER_SEC / HZ) * j;
+#elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
+ return (j + (HZ / MSEC_PER_SEC) - 1)/(HZ / MSEC_PER_SEC);
+#else
+# if BITS_PER_LONG == 32
+ return (HZ_TO_MSEC_MUL32 * j) >> HZ_TO_MSEC_SHR32;
+# else
+ return (j * HZ_TO_MSEC_NUM) / HZ_TO_MSEC_DEN;
+# endif
+#endif
+}
+extern unsigned int __jiffies_to_msecs(const unsigned long j);
+
+#define jiffies_to_msecs(x) \
+ (__builtin_constant_p(x) ? \
+ __inline_jiffies_to_msecs(x) : \
+ __jiffies_to_msecs(x))
+
+static __always_inline unsigned int
+__inline_jiffies_to_usecs(const unsigned long j)
+{
+#if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ)
+ return (USEC_PER_SEC / HZ) * j;
+#elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
+ return (j + (HZ / USEC_PER_SEC) - 1)/(HZ / USEC_PER_SEC);
+#else
+# if BITS_PER_LONG == 32
+ return (HZ_TO_USEC_MUL32 * j) >> HZ_TO_USEC_SHR32;
+# else
+ return (j * HZ_TO_USEC_NUM) / HZ_TO_USEC_DEN;
+# endif
+#endif
+}
+extern unsigned int __jiffies_to_usecs(const unsigned long j);
+
+#define jiffies_to_usecs(x) \
+ (__builtin_constant_p(x) ? \
+ __inline_jiffies_to_usecs(x) : \
+ __jiffies_to_usecs(x))
+
+/*
+ * When we convert to jiffies then we interpret incoming values
+ * the following way:
+ *
+ * - negative values mean 'infinite timeout' (MAX_JIFFY_OFFSET)
+ *
+ * - 'too large' values [that would result in larger than
+ * 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.
+ */
+static __always_inline unsigned long
+__inline_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
+}
+extern unsigned long __msecs_to_jiffies(const unsigned int m);
+
+#define msecs_to_jiffies(x) \
+ (__builtin_constant_p(x) ? \
+ __inline_msecs_to_jiffies(x) : \
+ __msecs_to_jiffies(x))
+
+static __always_inline unsigned long
+__inline_usecs_to_jiffies(const unsigned int u)
+{
+ if (u > jiffies_to_usecs(MAX_JIFFY_OFFSET))
+ return MAX_JIFFY_OFFSET;
+#if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ)
+ return (u + (USEC_PER_SEC / HZ) - 1) / (USEC_PER_SEC / HZ);
+#elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
+ return u * (HZ / USEC_PER_SEC);
+#else
+ return (USEC_TO_HZ_MUL32 * u + USEC_TO_HZ_ADJ32)
+ >> USEC_TO_HZ_SHR32;
+#endif
+}
+extern unsigned long __usecs_to_jiffies(const unsigned int u);
+
+#define usecs_to_jiffies(x) \
+ (__builtin_constant_p(x) ? \
+ __inline_usecs_to_jiffies(x) : \
+ __usecs_to_jiffies(x))
+
extern unsigned long timespec_to_jiffies(const struct timespec *value);
extern void jiffies_to_timespec(const unsigned long jiffies,
struct timespec *value);
diff --git a/kernel/time.c b/kernel/time.c
index d226c6a..b9d1024 100644
--- a/kernel/time.c
+++ b/kernel/time.c
@@ -228,41 +228,18 @@ EXPORT_SYMBOL(current_fs_time);

/*
* Convert jiffies to milliseconds and back.
- *
- * Avoid unnecessary multiplications/divisions in the
- * two most common HZ cases:
*/
-inline unsigned int jiffies_to_msecs(const unsigned long j)
+unsigned int __jiffies_to_msecs(const unsigned long j)
{
-#if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
- return (MSEC_PER_SEC / HZ) * j;
-#elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
- return (j + (HZ / MSEC_PER_SEC) - 1)/(HZ / MSEC_PER_SEC);
-#else
-# if BITS_PER_LONG == 32
- return (HZ_TO_MSEC_MUL32 * j) >> HZ_TO_MSEC_SHR32;
-# else
- return (j * HZ_TO_MSEC_NUM) / HZ_TO_MSEC_DEN;
-# endif
-#endif
+ return __inline_jiffies_to_msecs(j);
}
-EXPORT_SYMBOL(jiffies_to_msecs);
+EXPORT_SYMBOL(__jiffies_to_msecs);

-inline unsigned int jiffies_to_usecs(const unsigned long j)
+unsigned int __jiffies_to_usecs(const unsigned long j)
{
-#if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ)
- return (USEC_PER_SEC / HZ) * j;
-#elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
- return (j + (HZ / USEC_PER_SEC) - 1)/(HZ / USEC_PER_SEC);
-#else
-# if BITS_PER_LONG == 32
- return (HZ_TO_USEC_MUL32 * j) >> HZ_TO_USEC_SHR32;
-# else
- return (j * HZ_TO_USEC_NUM) / HZ_TO_USEC_DEN;
-# endif
-#endif
+ return __inline_jiffies_to_usecs(j);
}
-EXPORT_SYMBOL(jiffies_to_usecs);
+EXPORT_SYMBOL(__jiffies_to_usecs);

/**
* timespec_trunc - Truncate timespec to a granularity
@@ -411,76 +388,17 @@ struct timeval ns_to_timeval(const s64 nsec)
}
EXPORT_SYMBOL(ns_to_timeval);

-/*
- * When we convert to jiffies then we interpret incoming values
- * the following way:
- *
- * - negative values mean 'infinite timeout' (MAX_JIFFY_OFFSET)
- *
- * - 'too large' values [that would result in larger than
- * 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.
- */
-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 __inline_msecs_to_jiffies(m);
}
-EXPORT_SYMBOL(msecs_to_jiffies);
+EXPORT_SYMBOL(__msecs_to_jiffies);

-unsigned long usecs_to_jiffies(const unsigned int u)
+unsigned long __usecs_to_jiffies(const unsigned int u)
{
- if (u > jiffies_to_usecs(MAX_JIFFY_OFFSET))
- return MAX_JIFFY_OFFSET;
-#if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ)
- return (u + (USEC_PER_SEC / HZ) - 1) / (USEC_PER_SEC / HZ);
-#elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
- return u * (HZ / USEC_PER_SEC);
-#else
- return (USEC_TO_HZ_MUL32 * u + USEC_TO_HZ_ADJ32)
- >> USEC_TO_HZ_SHR32;
-#endif
+ return __inline_usecs_to_jiffies(u);
}
-EXPORT_SYMBOL(usecs_to_jiffies);
+EXPORT_SYMBOL(__usecs_to_jiffies);

/*
* The TICK_NSEC - 1 rounds up the value to the next resolution. Note