kernel_optimize_test/include/linux/time.h
Thomas Gleixner 660fd04f93 lib/vdso: Prepare for time namespace support
To support time namespaces in the vdso with a minimal impact on regular non
time namespace affected tasks, the namespace handling needs to be hidden in
a slow path.

The most obvious place is vdso_seq_begin(). If a task belongs to a time
namespace then the VVAR page which contains the system wide vdso data is
replaced with a namespace specific page which has the same layout as the
VVAR page. That page has vdso_data->seq set to 1 to enforce the slow path
and vdso_data->clock_mode set to VCLOCK_TIMENS to enforce the time
namespace handling path.

The extra check in the case that vdso_data->seq is odd, e.g. a concurrent
update of the vdso data is in progress, is not really affecting regular
tasks which are not part of a time namespace as the task is spin waiting
for the update to finish and vdso_data->seq to become even again.

If a time namespace task hits that code path, it invokes the corresponding
time getter function which retrieves the real VVAR page, reads host time
and then adds the offset for the requested clock which is stored in the
special VVAR page.

If VDSO time namespace support is disabled the whole magic is compiled out.

Initial testing shows that the disabled case is almost identical to the
host case which does not take the slow timens path. With the special timens
page installed the performance hit is constant time and in the range of
5-7%.

For the vdso functions which are not using the sequence count an
unconditional check for vdso_data->clock_mode is added which switches to
the real vdso when the clock_mode is VCLOCK_TIMENS.

[avagin: Make do_hres_timens() work with raw clocks too: choose vdso_data
 pointer by CS_RAW offset.]

Suggested-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrei Vagin <avagin@gmail.com>
Signed-off-by: Dmitry Safonov <dima@arista.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20191112012724.250792-21-dima@arista.com
2020-01-14 12:20:57 +01:00

120 lines
3.7 KiB
C

/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _LINUX_TIME_H
#define _LINUX_TIME_H
# include <linux/cache.h>
# include <linux/seqlock.h>
# include <linux/math64.h>
# include <linux/time64.h>
extern struct timezone sys_tz;
int get_timespec64(struct timespec64 *ts,
const struct __kernel_timespec __user *uts);
int put_timespec64(const struct timespec64 *ts,
struct __kernel_timespec __user *uts);
int get_itimerspec64(struct itimerspec64 *it,
const struct __kernel_itimerspec __user *uit);
int put_itimerspec64(const struct itimerspec64 *it,
struct __kernel_itimerspec __user *uit);
extern time64_t mktime64(const unsigned int year, const unsigned int mon,
const unsigned int day, const unsigned int hour,
const unsigned int min, const unsigned int sec);
/* Some architectures do not supply their own clocksource.
* This is mainly the case in architectures that get their
* inter-tick times by reading the counter on their interval
* timer. Since these timers wrap every tick, they're not really
* useful as clocksources. Wrapping them to act like one is possible
* but not very efficient. So we provide a callout these arches
* can implement for use with the jiffies clocksource to provide
* finer then tick granular time.
*/
#ifdef CONFIG_ARCH_USES_GETTIMEOFFSET
extern u32 (*arch_gettimeoffset)(void);
#endif
#ifdef CONFIG_POSIX_TIMERS
extern void clear_itimer(void);
#else
static inline void clear_itimer(void) {}
#endif
extern long do_utimes(int dfd, const char __user *filename, struct timespec64 *times, int flags);
/*
* Similar to the struct tm in userspace <time.h>, but it needs to be here so
* that the kernel source is self contained.
*/
struct tm {
/*
* the number of seconds after the minute, normally in the range
* 0 to 59, but can be up to 60 to allow for leap seconds
*/
int tm_sec;
/* the number of minutes after the hour, in the range 0 to 59*/
int tm_min;
/* the number of hours past midnight, in the range 0 to 23 */
int tm_hour;
/* the day of the month, in the range 1 to 31 */
int tm_mday;
/* the number of months since January, in the range 0 to 11 */
int tm_mon;
/* the number of years since 1900 */
long tm_year;
/* the number of days since Sunday, in the range 0 to 6 */
int tm_wday;
/* the number of days since January 1, in the range 0 to 365 */
int tm_yday;
};
void time64_to_tm(time64_t totalsecs, int offset, struct tm *result);
# include <linux/time32.h>
static inline bool itimerspec64_valid(const struct itimerspec64 *its)
{
if (!timespec64_valid(&(its->it_interval)) ||
!timespec64_valid(&(its->it_value)))
return false;
return true;
}
/**
* time_after32 - compare two 32-bit relative times
* @a: the time which may be after @b
* @b: the time which may be before @a
*
* time_after32(a, b) returns true if the time @a is after time @b.
* time_before32(b, a) returns true if the time @b is before time @a.
*
* Similar to time_after(), compare two 32-bit timestamps for relative
* times. This is useful for comparing 32-bit seconds values that can't
* be converted to 64-bit values (e.g. due to disk format or wire protocol
* issues) when it is known that the times are less than 68 years apart.
*/
#define time_after32(a, b) ((s32)((u32)(b) - (u32)(a)) < 0)
#define time_before32(b, a) time_after32(a, b)
/**
* time_between32 - check if a 32-bit timestamp is within a given time range
* @t: the time which may be within [l,h]
* @l: the lower bound of the range
* @h: the higher bound of the range
*
* time_before32(t, l, h) returns true if @l <= @t <= @h. All operands are
* treated as 32-bit integers.
*
* Equivalent to !(time_before32(@t, @l) || time_after32(@t, @h)).
*/
#define time_between32(t, l, h) ((u32)(h) - (u32)(l) >= (u32)(t) - (u32)(l))
struct timens_offset {
s64 sec;
u64 nsec;
};
#endif