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2760105516
linux/kernel/time
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Cassio Neri 2760105516 time: Improve performance of time64_to_tm() 
The current implementation of time64_to_tm() contains unnecessary loops,
branches and look-up tables. The new one uses an arithmetic-based algorithm
appeared in [1] and is approximately 3x faster (YMMV).

The drawback is that the new code isn't intuitive and contains many 'magic
numbers' (not unusual for this type of algorithm). However, [1] justifies
all those numbers and, given this function's history, the code is unlikely
to need much maintenance, if any at all.

Add a KUnit test for it which checks every day in a 160,000 years interval
centered at 1970-01-01 against the expected result.

[1] Neri, Schneider, "Euclidean Affine Functions and Applications to
Calendar Algorithms". https://arxiv.org/abs/2102.06959

Signed-off-by: Cassio Neri <cassio.neri@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20210622213616.313046-1-cassio.neri@gmail.com
2021-06-24 11:51:59 +02:00
..
alarmtimer.c alarmtimer: Check RTC features instead of ops 2021-05-11 21:28:04 +02:00
clockevents.c clockevents: Use list_move() instead of list_del()/list_add() 2021-06-22 17:16:46 +02:00
clocksource-wdtest.c clocksource: Provide kernel module to test clocksource watchdog 2021-06-22 16:53:17 +02:00
clocksource.c clocksource: Print deviation in nanoseconds when a clocksource becomes unstable 2021-06-22 16:53:17 +02:00
hrtimer.c The time and timers updates contain: 2021-04-26 09:54:03 -07:00
itimer.c time: Prevent undefined behaviour in timespec64_to_ns() 2020-10-26 11:48:11 +01:00
jiffies.c clocksource: Reduce clocksource-skew threshold 2021-06-22 16:53:16 +02:00
Kconfig time: Improve performance of time64_to_tm() 2021-06-24 11:51:59 +02:00
Makefile time: Improve performance of time64_to_tm() 2021-06-24 11:51:59 +02:00
namespace.c timens: Delete no-op time_ns_init() 2021-02-05 19:32:09 +01:00
ntp_internal.h ntp: Make the RTC synchronization more reliable 2020-12-11 10:40:52 +01:00
ntp.c timekeeping, clocksource: Fix various typos in comments 2021-03-22 23:06:48 +01:00
posix-clock.c posix-clocks: Rename the clock_get() callback to clock_get_timespec() 2020-01-14 12:20:49 +01:00
posix-cpu-timers.c The time and timers updates contain: 2021-04-26 09:54:03 -07:00
posix-stubs.c posix-timers: Make clock_nanosleep() time namespace aware 2020-01-14 12:20:55 +01:00
posix-timers.c posix-timers: Preserve return value in clock_adjtime32() 2021-04-17 14:55:06 +02:00
posix-timers.h posix-clocks: Introduce clock_get_ktime() callback 2020-01-14 12:20:51 +01:00
sched_clock.c time/sched_clock: Mark sched_clock_read_begin/retry() as notrace 2020-10-26 11:34:31 +01:00
test_udelay.c time/debug: Remove dentry pointer for debugfs 2021-03-18 11:20:26 +01:00
tick-broadcast-hrtimer.c timekeeping, clocksource: Fix various typos in comments 2021-03-22 23:06:48 +01:00
tick-broadcast.c timer_list: Print name of per-cpu wakeup device 2021-05-31 17:04:49 +02:00
tick-common.c tick/broadcast: Prefer per-cpu oneshot wakeup timers to broadcast 2021-05-31 17:04:45 +02:00
tick-internal.h timer_list: Print name of per-cpu wakeup device 2021-05-31 17:04:49 +02:00
tick-legacy.c timekeeping: remove xtime_update 2020-10-30 21:57:07 +01:00
tick-oneshot.c timekeeping, clocksource: Fix various typos in comments 2021-03-22 23:06:48 +01:00
tick-sched.c Power management updates for 5.13-rc1 2021-04-26 15:10:25 -07:00
tick-sched.h timekeeping, clocksource: Fix various typos in comments 2021-03-22 23:06:48 +01:00
time_test.c time: Improve performance of time64_to_tm() 2021-06-24 11:51:59 +02:00
time.c timekeeping, clocksource: Fix various typos in comments 2021-03-22 23:06:48 +01:00
timeconst.bc time: Add SPDX license identifiers 2018-11-23 11:51:20 +01:00
timeconv.c time: Improve performance of time64_to_tm() 2021-06-24 11:51:59 +02:00
timecounter.c time/timecounter: Mark 1st argument of timecounter_cyc2time() as const 2021-04-16 21:03:50 +02:00
timekeeping_debug.c timekeeping/debug: No need to check return value of debugfs_create functions 2019-01-29 20:08:41 +01:00
timekeeping_internal.h timekeeping/vsyscall: Provide vdso_update_begin/end() 2020-08-06 10:57:30 +02:00
timekeeping.c ARM: 2021-05-01 10:14:08 -07:00
timekeeping.h asm-generic: cross-architecture timer cleanup 2020-12-16 00:07:17 -08:00
timer_list.c timer_list: Print name of per-cpu wakeup device 2021-05-31 17:04:49 +02:00
timer.c timekeeping, clocksource: Fix various typos in comments 2021-03-22 23:06:48 +01:00
vsyscall.c timekeeping, clocksource: Fix various typos in comments 2021-03-22 23:06:48 +01:00