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Subject[PATCH 2/3] time: allow gcc to fold constants when using msecs_to_jiffies
Date
The majority of the msecs_to_jiffies() users in the kernel are passing in
constants which would allow gcc to do constant folding by checking with
__builtin_constant_p() in msecs_to_jiffies().

The original msecs_to_jiffies is renamed to __msecs_to_jiffies and aside
from the removal of the check for negative values being moved out, is
unaltered.

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.

Patch was compile and boot tested (x86_64) and a few msecs_to_jiffies()
locations verified by inspection of the .lst files.

Patch is against 4.0-rc6 (localversion-next is -next-20150402)

include/linux/jiffies.h | 29 ++++++++++++++++++++++++++++-
kernel/time/time.c | 13 +++++--------
2 files changed, 33 insertions(+), 9 deletions(-)

diff --git a/include/linux/jiffies.h b/include/linux/jiffies.h
index c367cbd..dcd8ba5 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 +289,33 @@ 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);
+static inline unsigned long msecs_to_jiffies(const unsigned int m)
+{
+ /*
+ * Negative value, means infinite timeout:
+ */
+ if ((int)m < 0)
+ return MAX_JIFFY_OFFSET;
+
+ if (__builtin_constant_p(m)) {
+#if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
+ return (m + (MSEC_PER_SEC / HZ) - 1) / (MSEC_PER_SEC / HZ);
+#elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
+ if (m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
+ return MAX_JIFFY_OFFSET;
+ return m * (HZ / MSEC_PER_SEC);
+#else
+ 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
+ } else
+ 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..3797540 100644
--- a/kernel/time/time.c
+++ b/kernel/time/time.c
@@ -488,6 +488,8 @@ EXPORT_SYMBOL(ns_to_timespec64);
* the following way:
*
* - negative values mean 'infinite timeout' (MAX_JIFFY_OFFSET)
+ * negative values are handled in msecs_to_jiffies in
+ * include/linux/jiffies.h
*
* - 'too large' values [that would result in larger than
* MAX_JIFFY_OFFSET values] mean 'infinite timeout' too.
@@ -496,15 +498,10 @@ EXPORT_SYMBOL(ns_to_timespec64);
* 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
@@ -537,7 +534,7 @@ unsigned long msecs_to_jiffies(const unsigned int m)
>> MSEC_TO_HZ_SHR32;
#endif
}
-EXPORT_SYMBOL(msecs_to_jiffies);
+EXPORT_SYMBOL(__msecs_to_jiffies);

unsigned long usecs_to_jiffies(const unsigned int u)
{
--
1.7.10.4


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