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Commit 24e4a8c3 authored by John Stultz's avatar John Stultz
Browse files

ktime: Kill non-scalar ktime_t implementation for 2038 



The non-scalar ktime_t implementation is basically a timespec
which has to be changed to support dates past 2038 on 32bit
systems.

This patch removes the non-scalar ktime_t implementation, forcing
the scalar s64 nanosecond version on all architectures.

This may have additional performance overhead on some 32bit
systems when converting between ktime_t and timespec structures,
however the majority of 32bit systems (arm and i386) were already
using scalar ktime_t, so no performance regressions will be seen
on those platforms.

On affected platforms, I'm open to finding optimizations, including
avoiding converting to timespecs where possible.

[ tglx: We can now cleanup the ktime_t.tv64 mess, but thats a
  different issue and we can throw a coccinelle script at it ]

Signed-off-by: default avatarJohn Stultz <john.stultz@linaro.org>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarJohn Stultz <john.stultz@linaro.org>
parent 76f41088

arch/arm/Kconfig

+0 −1
Original line number Diff line number Diff line
@@ -64,7 +64,6 @@ config ARM 
	select HAVE_UID16

	select HAVE_VIRT_CPU_ACCOUNTING_GEN

	select IRQ_FORCED_THREADING

	select KTIME_SCALAR

	select MODULES_USE_ELF_REL

	select NO_BOOTMEM

	select OLD_SIGACTION

arch/hexagon/Kconfig

+0 −1
Original line number Diff line number Diff line
@@ -23,7 +23,6 @@ config HEXAGON 
	select GENERIC_IOMAP

	select GENERIC_SMP_IDLE_THREAD

	select STACKTRACE_SUPPORT

	select KTIME_SCALAR

	select GENERIC_CLOCKEVENTS

	select GENERIC_CLOCKEVENTS_BROADCAST

	select MODULES_USE_ELF_RELA

arch/s390/Kconfig

+0 −1
Original line number Diff line number Diff line
@@ -137,7 +137,6 @@ config S390 
	select HAVE_SYSCALL_TRACEPOINTS

	select HAVE_UID16 if 32BIT

	select HAVE_VIRT_CPU_ACCOUNTING

	select KTIME_SCALAR if 32BIT

	select MODULES_USE_ELF_RELA

	select NO_BOOTMEM

	select OLD_SIGACTION

arch/x86/Kconfig

+0 −1
Original line number Diff line number Diff line
@@ -111,7 +111,6 @@ config X86 
	select ARCH_CLOCKSOURCE_DATA

	select GENERIC_CLOCKEVENTS_BROADCAST if X86_64 || (X86_32 && X86_LOCAL_APIC)

	select GENERIC_TIME_VSYSCALL

	select KTIME_SCALAR if X86_32

	select GENERIC_STRNCPY_FROM_USER

	select GENERIC_STRNLEN_USER

	select HAVE_CONTEXT_TRACKING if X86_64

include/linux/ktime.h

+1 −172
Original line number Diff line number Diff line
@@ -27,43 +27,19 @@ 
/*

 * ktime_t:

 *

 * On 64-bit CPUs a single 64-bit variable is used to store the hrtimers

 * A single 64-bit variable is used to store the hrtimers

 * internal representation of time values in scalar nanoseconds. The

 * design plays out best on 64-bit CPUs, where most conversions are

 * NOPs and most arithmetic ktime_t operations are plain arithmetic

 * operations.

 *

 * On 32-bit CPUs an optimized representation of the timespec structure

 * is used to avoid expensive conversions from and to timespecs. The

 * endian-aware order of the tv struct members is chosen to allow

 * mathematical operations on the tv64 member of the union too, which

 * for certain operations produces better code.

 *

 * For architectures with efficient support for 64/32-bit conversions the

 * plain scalar nanosecond based representation can be selected by the

 * config switch CONFIG_KTIME_SCALAR.

 */

union ktime {

	s64	tv64;

#if BITS_PER_LONG != 64 && !defined(CONFIG_KTIME_SCALAR)

	struct {

# ifdef __BIG_ENDIAN

	s32	sec, nsec;

# else

	s32	nsec, sec;

# endif

	} tv;

#endif

};



typedef union ktime ktime_t;		/* Kill this */



/*

 * ktime_t definitions when using the 64-bit scalar representation:

 */



#if (BITS_PER_LONG == 64) || defined(CONFIG_KTIME_SCALAR)



/**

 * ktime_set - Set a ktime_t variable from a seconds/nanoseconds value

 * @secs:	seconds to set
@@ -123,153 +99,6 @@ static inline ktime_t timeval_to_ktime(struct timeval tv) 
/* Convert ktime_t to nanoseconds - NOP in the scalar storage format: */

#define ktime_to_ns(kt)			((kt).tv64)



#else	/* !((BITS_PER_LONG == 64) || defined(CONFIG_KTIME_SCALAR)) */



/*

 * Helper macros/inlines to get the ktime_t math right in the timespec

 * representation. The macros are sometimes ugly - their actual use is

 * pretty okay-ish, given the circumstances. We do all this for

 * performance reasons. The pure scalar nsec_t based code was nice and

 * simple, but created too many 64-bit / 32-bit conversions and divisions.

 *

 * Be especially aware that negative values are represented in a way

 * that the tv.sec field is negative and the tv.nsec field is greater

 * or equal to zero but less than nanoseconds per second. This is the

 * same representation which is used by timespecs.

 *

 *   tv.sec < 0 and 0 >= tv.nsec < NSEC_PER_SEC

 */



/* Set a ktime_t variable to a value in sec/nsec representation: */

static inline ktime_t ktime_set(const long secs, const unsigned long nsecs)

{

	return (ktime_t) { .tv = { .sec = secs, .nsec = nsecs } };

}



/**

 * ktime_sub - subtract two ktime_t variables

 * @lhs:	minuend

 * @rhs:	subtrahend

 *

 * Return: The remainder of the subtraction.

 */

static inline ktime_t ktime_sub(const ktime_t lhs, const ktime_t rhs)

{

	ktime_t res;



	res.tv64 = lhs.tv64 - rhs.tv64;

	if (res.tv.nsec < 0)

		res.tv.nsec += NSEC_PER_SEC;



	return res;

}



/**

 * ktime_add - add two ktime_t variables

 * @add1:	addend1

 * @add2:	addend2

 *

 * Return: The sum of @add1 and @add2.

 */

static inline ktime_t ktime_add(const ktime_t add1, const ktime_t add2)

{

	ktime_t res;



	res.tv64 = add1.tv64 + add2.tv64;

	/*

	 * performance trick: the (u32) -NSEC gives 0x00000000Fxxxxxxx

	 * so we subtract NSEC_PER_SEC and add 1 to the upper 32 bit.

	 *

	 * it's equivalent to:

	 *   tv.nsec -= NSEC_PER_SEC

	 *   tv.sec ++;

	 */

	if (res.tv.nsec >= NSEC_PER_SEC)

		res.tv64 += (u32)-NSEC_PER_SEC;



	return res;

}



/**

 * ktime_add_ns - Add a scalar nanoseconds value to a ktime_t variable

 * @kt:		addend

 * @nsec:	the scalar nsec value to add

 *

 * Return: The sum of @kt and @nsec in ktime_t format.

 */

extern ktime_t ktime_add_ns(const ktime_t kt, u64 nsec);



/**

 * ktime_sub_ns - Subtract a scalar nanoseconds value from a ktime_t variable

 * @kt:		minuend

 * @nsec:	the scalar nsec value to subtract

 *

 * Return: The subtraction of @nsec from @kt in ktime_t format.

 */

extern ktime_t ktime_sub_ns(const ktime_t kt, u64 nsec);



/**

 * timespec_to_ktime - convert a timespec to ktime_t format

 * @ts:		the timespec variable to convert

 *

 * Return: A ktime_t variable with the converted timespec value.

 */

static inline ktime_t timespec_to_ktime(const struct timespec ts)

{

	return (ktime_t) { .tv = { .sec = (s32)ts.tv_sec,

			   	   .nsec = (s32)ts.tv_nsec } };

}



/**

 * timeval_to_ktime - convert a timeval to ktime_t format

 * @tv:		the timeval variable to convert

 *

 * Return: A ktime_t variable with the converted timeval value.

 */

static inline ktime_t timeval_to_ktime(const struct timeval tv)

{

	return (ktime_t) { .tv = { .sec = (s32)tv.tv_sec,

				   .nsec = (s32)(tv.tv_usec *

						 NSEC_PER_USEC) } };

}



/**

 * ktime_to_timespec - convert a ktime_t variable to timespec format

 * @kt:		the ktime_t variable to convert

 *

 * Return: The timespec representation of the ktime value.

 */

static inline struct timespec ktime_to_timespec(const ktime_t kt)

{

	return (struct timespec) { .tv_sec = (time_t) kt.tv.sec,

				   .tv_nsec = (long) kt.tv.nsec };

}



/**

 * ktime_to_timeval - convert a ktime_t variable to timeval format

 * @kt:		the ktime_t variable to convert

 *

 * Return: The timeval representation of the ktime value.

 */

static inline struct timeval ktime_to_timeval(const ktime_t kt)

{

	return (struct timeval) {

		.tv_sec = (time_t) kt.tv.sec,

		.tv_usec = (suseconds_t) (kt.tv.nsec / NSEC_PER_USEC) };

}



/**

 * ktime_to_ns - convert a ktime_t variable to scalar nanoseconds

 * @kt:		the ktime_t variable to convert

 *

 * Return: The scalar nanoseconds representation of @kt.

 */

static inline s64 ktime_to_ns(const ktime_t kt)

{

	return (s64) kt.tv.sec * NSEC_PER_SEC + kt.tv.nsec;

}



#endif	/* !((BITS_PER_LONG == 64) || defined(CONFIG_KTIME_SCALAR)) */



/**

 * ktime_equal - Compares two ktime_t variables to see if they are equal