time: Improve performance of time64_to_tm() (27601055) · Commits · EulixOS / Software / Kernel

kernel/time/Kconfig

+9 −0

Original line number	Diff line number	Diff line
		@@ -64,6 +64,15 @@ config LEGACY_TIMER_TICK
		lack support for the generic clockevent framework.
		New platforms should use generic clockevents instead.

		config TIME_KUNIT_TEST
		tristate "KUnit test for kernel/time functions" if !KUNIT_ALL_TESTS
		depends on KUNIT
		default KUNIT_ALL_TESTS
		help
		Enable this option to test RTC library functions.

		If unsure, say N.

		if GENERIC_CLOCKEVENTS
		menu "Timers subsystem"

kernel/time/Makefile

+1 −0

Original line number	Diff line number	Diff line
		@@ -22,3 +22,4 @@ obj-$(CONFIG_DEBUG_FS) += timekeeping_debug.o
		obj-$(CONFIG_TEST_UDELAY) += test_udelay.o
		obj-$(CONFIG_TIME_NS) += namespace.o
		obj-$(CONFIG_TEST_CLOCKSOURCE_WATCHDOG) += clocksource-wdtest.o
		obj-$(CONFIG_TIME_KUNIT_TEST) += time_test.o

kernel/time/time_test.c

0 → 100644

+98 −0

Original line number	Diff line number	Diff line
		// SPDX-License-Identifier: LGPL-2.1+

		#include <kunit/test.h>
		#include <linux/time.h>

		/*
		* Traditional implementation of leap year evaluation.
		*/
		static bool is_leap(long year)
		{
		return year % 4 == 0 && (year % 100 != 0 \|\| year % 400 == 0);
		}

		/*
		* Gets the last day of a month.
		*/
		static int last_day_of_month(long year, int month)
		{
		if (month == 2)
		return 28 + is_leap(year);
		if (month == 4 \|\| month == 6 \|\| month == 9 \|\| month == 11)
		return 30;
		return 31;
		}

		/*
		* Advances a date by one day.
		*/
		static void advance_date(long year, int month, int mday, int yday)
		{
		if (mday != last_day_of_month(year, *month)) {
		++*mday;
		++*yday;
		return;
		}

		*mday = 1;
		if (*month != 12) {
		++*month;
		++*yday;
		return;
		}

		*month = 1;
		*yday = 0;
		++*year;
		}

		/*
		* Checks every day in a 160000 years interval centered at 1970-01-01
		* against the expected result.
		*/
		static void time64_to_tm_test_date_range(struct kunit *test)
		{
		/*
		* 80000 years = (80000 / 400) * 400 years
		* = (80000 / 400) * 146097 days
		* = (80000 / 400) * 146097 * 86400 seconds
		*/
		time64_t total_secs = ((time64_t) 80000) / 400 * 146097 * 86400;
		long year = 1970 - 80000;
		int month = 1;
		int mdday = 1;
		int yday = 0;

		struct tm result;
		time64_t secs;
		s64 days;

		for (secs = -total_secs; secs <= total_secs; secs += 86400) {

		time64_to_tm(secs, 0, &result);

		days = div_s64(secs, 86400);

		#define FAIL_MSG "%05ld/%02d/%02d (%2d) : %ld", \
		year, month, mdday, yday, days

		KUNIT_ASSERT_EQ_MSG(test, year - 1900, result.tm_year, FAIL_MSG);
		KUNIT_ASSERT_EQ_MSG(test, month - 1, result.tm_mon, FAIL_MSG);
		KUNIT_ASSERT_EQ_MSG(test, mdday, result.tm_mday, FAIL_MSG);
		KUNIT_ASSERT_EQ_MSG(test, yday, result.tm_yday, FAIL_MSG);

		advance_date(&year, &month, &mdday, &yday);
		}
		}

		static struct kunit_case time_test_cases[] = {
		KUNIT_CASE(time64_to_tm_test_date_range),
		{}
		};

		static struct kunit_suite time_test_suite = {
		.name = "time_test_cases",
		.test_cases = time_test_cases,
		};

		kunit_test_suite(time_test_suite);

kernel/time/timeconv.c

+70 −58

Original line number	Diff line number	Diff line
		@@ -22,47 +22,16 @@

		/*
		* Converts the calendar time to broken-down time representation
		* Based on code from glibc-2.6
		*
		* 2009-7-14:
		* Moved from glibc-2.6 to kernel by Zhaolei<zhaolei@cn.fujitsu.com>
		* 2021-06-02:
		* Reimplemented by Cassio Neri <cassio.neri@gmail.com>
		*/

		#include <linux/time.h>
		#include <linux/module.h>

		/*
		* Nonzero if YEAR is a leap year (every 4 years,
		* except every 100th isn't, and every 400th is).
		*/
		static int __isleap(long year)
		{
		return (year) % 4 == 0 && ((year) % 100 != 0 \|\| (year) % 400 == 0);
		}

		/* do a mathdiv for long type */
		static long math_div(long a, long b)
		{
		return a / b - (a % b < 0);
		}

		/* How many leap years between y1 and y2, y1 must less or equal to y2 */
		static long leaps_between(long y1, long y2)
		{
		long leaps1 = math_div(y1 - 1, 4) - math_div(y1 - 1, 100)
		+ math_div(y1 - 1, 400);
		long leaps2 = math_div(y2 - 1, 4) - math_div(y2 - 1, 100)
		+ math_div(y2 - 1, 400);
		return leaps2 - leaps1;
		}

		/* How many days come before each month (0-12). */
		static const unsigned short __mon_yday[2][13] = {
		/* Normal years. */
		{0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365},
		/* Leap years. */
		{0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366}
		};
		#include <linux/kernel.h>

		#define SECS_PER_HOUR (60 * 60)
		#define SECS_PER_DAY (SECS_PER_HOUR * 24)
		@@ -77,9 +46,11 @@ static const unsigned short __mon_yday[2][13] = {
		*/
		void time64_to_tm(time64_t totalsecs, int offset, struct tm *result)
		{
		long days, rem, y;
		u32 u32tmp, day_of_century, year_of_century, day_of_year, month, day;
		u64 u64tmp, udays, century, year;
		bool is_Jan_or_Feb, is_leap_year;
		long days, rem;
		int remainder;
		const unsigned short *ip;

		days = div_s64_rem(totalsecs, SECS_PER_DAY, &remainder);
		rem = remainder;
		@@ -103,27 +74,68 @@ void time64_to_tm(time64_t totalsecs, int offset, struct tm *result)
		if (result->tm_wday < 0)
		result->tm_wday += 7;

		y = 1970;
		/*
		* The following algorithm is, basically, Proposition 6.3 of Neri
		* and Schneider [1]. In a few words: it works on the computational
		* (fictitious) calendar where the year starts in March, month = 2
		* (*), and finishes in February, month = 13. This calendar is
		* mathematically convenient because the day of the year does not
		* depend on whether the year is leap or not. For instance:
		*
		* March 1st 0-th day of the year;
		* ...
		* April 1st 31-st day of the year;
		* ...
		* January 1st 306-th day of the year; (Important!)
		* ...
		* February 28th 364-th day of the year;
		* February 29th 365-th day of the year (if it exists).
		*
		* After having worked out the date in the computational calendar
		* (using just arithmetics) it's easy to convert it to the
		* corresponding date in the Gregorian calendar.
		*
		* [1] "Euclidean Affine Functions and Applications to Calendar
		* Algorithms". https://arxiv.org/abs/2102.06959
		*
		* (*) The numbering of months follows tm more closely and thus,
		* is slightly different from [1].
		*/

		while (days < 0 \|\| days >= (__isleap(y) ? 366 : 365)) {
		/* Guess a corrected year, assuming 365 days per year. */
		long yg = y + math_div(days, 365);
		udays = ((u64) days) + 2305843009213814918ULL;

		/* Adjust DAYS and Y to match the guessed year. */
		days -= (yg - y) * 365 + leaps_between(y, yg);
		y = yg;
		}
		u64tmp = 4 * udays + 3;
		century = div64_u64_rem(u64tmp, 146097, &u64tmp);
		day_of_century = (u32) (u64tmp / 4);

		result->tm_year = y - 1900;
		u32tmp = 4 * day_of_century + 3;
		u64tmp = 2939745ULL * u32tmp;
		year_of_century = upper_32_bits(u64tmp);
		day_of_year = lower_32_bits(u64tmp) / 2939745 / 4;

		result->tm_yday = days;
		year = 100 * century + year_of_century;
		is_leap_year = year_of_century ? !(year_of_century % 4) : !(century % 4);

		ip = __mon_yday[__isleap(y)];
		for (y = 11; days < ip[y]; y--)
		continue;
		days -= ip[y];
		u32tmp = 2141 * day_of_year + 132377;
		month = u32tmp >> 16;
		day = ((u16) u32tmp) / 2141;

		result->tm_mon = y;
		result->tm_mday = days + 1;
		/*
		* Recall that January 1st is the 306-th day of the year in the
		* computational (not Gregorian) calendar.
		*/
		is_Jan_or_Feb = day_of_year >= 306;

		/* Convert to the Gregorian calendar and adjust to Unix time. */
		year = year + is_Jan_or_Feb - 6313183731940000ULL;
		month = is_Jan_or_Feb ? month - 12 : month;
		day = day + 1;
		day_of_year += is_Jan_or_Feb ? -306 : 31 + 28 + is_leap_year;

		/* Convert to tm's format. */
		result->tm_year = (long) (year - 1900);
		result->tm_mon = (int) month;
		result->tm_mday = (int) day;
		result->tm_yday = (int) day_of_year;
		}
		EXPORT_SYMBOL(time64_to_tm);