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ktime: Optimize ktime_divns for constant divisors

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[ Upstream commit 8b618628b2bf83512fc8df5e8672619d65adfdfb ]

At least on ARM, do_div() is optimized to turn constant divisors into
an inline multiplication by the reciprocal value at compile time.
However this optimization is missed entirely whenever ktime_divns() is
used and the slow out-of-line division code is used all the time.

Let ktime_divns() use do_div() inline whenever the divisor is constant
and small enough.  This will make things like ktime_to_us() and
ktime_to_ms() much faster.

Change-Id: I6a672b10d6d6b373b327f9548135ededfd1e1835
Cc: Arnd Bergmann <arnd.bergmann@linaro.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Nicolas Pitre <nico@linaro.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Kevin F. Haggerty <haggertk@lineageos.org>
This commit is contained in:
Nicolas Pitre
2021-06-19 16:25:32 +02:00
committed by matteo0026
parent 79485b48e2
commit f2bbaf99a1
2 changed files with 13 additions and 3 deletions
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kernel/hrtimer.c
+2 -2
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@@ -323,7 +323,7 @@ EXPORT_SYMBOL_GPL(ktime_sub_ns);
/*
* Divide a ktime value by a nanosecond value
*/
u64 ktime_divns(const ktime_t kt, s64 div)
u64 __ktime_divns(const ktime_t kt, s64 div)
{
u64 dclc;
int sft = 0;
@@ -339,7 +339,7 @@ u64 ktime_divns(const ktime_t kt, s64 div)
return dclc;
}
EXPORT_SYMBOL_GPL(ktime_divns);
EXPORT_SYMBOL_GPL(__ktime_divns);
#endif /* BITS_PER_LONG >= 64 */
/*