[PATCH 2/3 V3] time: refactor msecs_to_jiffies

Nicholas Mc Guire
2015-05-18T12:27:48Z

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.

Patch was build tested for:
arm - imx_v6_v7_defconfig, vexpress_defconfig
cris - etrax-100lx_v2_defconfig
m68k - multi_defconfig
mips32 - ar7_defconfig,
mips64 - loongson3_defconfig
powerpc - 44x/virtex5_defconfig
powerpc64 - powerpc64_defconfig
sh - se7780_defconfig,
sparc32 - sparc32_defconfig
sparc64 - sparc64_defconfig
x86 64 - x86_64_defconfig,
and boot/run tested for
x86 64 - x86_64_defconfig on an i3

Patch is against 4.1-rc3 (localversion-next is -next-20150518)

Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
---

Thanks to Joe Perches <joe@perches.com> for suggesting this approach
and for his review comments on the first attempts and for his simple
test-case that helped after I confused my self with .lst files.

V3: refactoring of time.c/jiffies.h as requested by Thomas Gleixner
<tglx@linutronix.de> without actually adding the builtin_constant_p()
check

include/linux/jiffies.h | 64 ++++++++++++++++++++++++++++++++++++++++++++++-
kernel/time/time.c | 59 ++++++++++++++-----------------------------
2 files changed, 82 insertions(+), 41 deletions(-)

diff --git a/include/linux/jiffies.h b/include/linux/jiffies.h
index c367cbd..b41e026e 100644
--- a/include/linux/jiffies.h
+++ b/include/linux/jiffies.h
@@ -7,6 +7,7 @@
#include <linux/time.h>
#include <linux/timex.h>
#include <asm/param.h> /* for HZ */
+#include <generated/timeconst.h>

/*
* The following defines establish the engineering parameters of the PLL
@@ -288,7 +289,68 @@ static inline u64 jiffies_to_nsecs(const unsigned long j)
return (u64)jiffies_to_usecs(j) * NSEC_PER_USEC;
}

-extern unsigned long msecs_to_jiffies(const unsigned int m);
+extern unsigned long __msecs_to_jiffies(const unsigned int m);
+#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:
+ */
+static inline unsigned long _msecs_to_jiffies(const unsigned int m)
+{
+ 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:
+ */
+static inline unsigned long _msecs_to_jiffies(const unsigned int m)
+{
+ 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:
+ */
+static inline unsigned long _msecs_to_jiffies(const unsigned int m)
+{
+ 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
+/**
+ * msecs_to_jiffies: - convert milliseconds to jiffies
+ * @m: time in milliseconds
+ *
+ * conversion is done as follows:
+ *
+ * - 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 and
+ * handling any 32-bit overflows.
+ * for the details see __msecs_to_jiffies()
+ *
+ * the HZ range specific helpers _msecs_to_jiffies() are called from
+ * __msecs_to_jiffies().
+ */
+static inline unsigned long msecs_to_jiffies(const unsigned int m)
+{
+ return __msecs_to_jiffies(m);
+}
+
extern unsigned long usecs_to_jiffies(const unsigned int u);
extern unsigned long timespec_to_jiffies(const struct timespec *value);
extern void jiffies_to_timespec(const unsigned long jiffies,
diff --git a/kernel/time/time.c b/kernel/time/time.c
index 4fa1d26..884bb8e 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)
{
--
1.7.10.4