linux/kernel/time/timekeeping.h
Thomas Gleixner e5d4d1756b timekeeping: Split jiffies seqlock
seqlock consists of a sequence counter and a spinlock_t which is used to
serialize the writers. spinlock_t is substituted by a "sleeping" spinlock
on PREEMPT_RT enabled kernels which breaks the usage in the timekeeping
code as the writers are executed in hard interrupt and therefore
non-preemptible context even on PREEMPT_RT.

The spinlock in seqlock cannot be unconditionally replaced by a
raw_spinlock_t as many seqlock users have nesting spinlock sections or
other code which is not suitable to run in truly atomic context on RT.

Instead of providing a raw_seqlock API for a single use case, open code the
seqlock for the jiffies use case and implement it with a raw_spinlock_t and
a sequence counter.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200321113242.120587764@linutronix.de
2020-03-21 16:00:23 +01:00

34 lines
926 B
C

/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _KERNEL_TIME_TIMEKEEPING_H
#define _KERNEL_TIME_TIMEKEEPING_H
/*
* Internal interfaces for kernel/time/
*/
extern ktime_t ktime_get_update_offsets_now(unsigned int *cwsseq,
ktime_t *offs_real,
ktime_t *offs_boot,
ktime_t *offs_tai);
extern int timekeeping_valid_for_hres(void);
extern u64 timekeeping_max_deferment(void);
extern void timekeeping_warp_clock(void);
extern int timekeeping_suspend(void);
extern void timekeeping_resume(void);
#ifdef CONFIG_GENERIC_SCHED_CLOCK
extern int sched_clock_suspend(void);
extern void sched_clock_resume(void);
#else
static inline int sched_clock_suspend(void) { return 0; }
static inline void sched_clock_resume(void) { }
#endif
extern void do_timer(unsigned long ticks);
extern void update_wall_time(void);
extern raw_spinlock_t jiffies_lock;
extern seqcount_t jiffies_seq;
#define CS_NAME_LEN 32
#endif