Commit 20c7b582 authored by Thomas Gleixner's avatar Thomas Gleixner
Browse files

timekeeping: Move shadow_timekeeper into tk_core 



tk_core requires shadow_timekeeper to allow timekeeping_advance() updating
without holding the timekeeper sequence count write locked. This allows the
readers to make progress up to the actual update where the shadow
timekeeper is copied over to the real timekeeper.

As long as there is only a single timekeeper, having them separate is
fine. But when the timekeeper infrastructure will be reused for per ptp
clock timekeepers, shadow_timekeeper needs to be part of tk_core.

No functional change.

Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarAnna-Maria Behnsen <anna-maria@linutronix.de>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Acked-by: default avatarJohn Stultz <jstultz@google.com>
Link: https://lore.kernel.org/all/20241009-devel-anna-maria-b4-timers-ptp-timekeeping-v2-7-554456a44a15@linutronix.de
parent 6860d28c

kernel/time/timekeeping.c

+3 −4
Original line number Diff line number Diff line
@@ -50,11 +50,11 @@ DEFINE_RAW_SPINLOCK(timekeeper_lock); 
static struct {

	seqcount_raw_spinlock_t	seq;

	struct timekeeper	timekeeper;

	struct timekeeper	shadow_timekeeper;

} tk_core ____cacheline_aligned = {

	.seq = SEQCNT_RAW_SPINLOCK_ZERO(tk_core.seq, &timekeeper_lock),

};



static struct timekeeper shadow_timekeeper;



/* flag for if timekeeping is suspended */

int __read_mostly timekeeping_suspended;
@@ -795,8 +795,7 @@ static void timekeeping_update(struct timekeeper *tk, unsigned int action) 
	 * timekeeper structure on the next update with stale data

	 */

	if (action & TK_MIRROR)

		memcpy(&shadow_timekeeper, &tk_core.timekeeper,

		       sizeof(tk_core.timekeeper));

		memcpy(&tk_core.shadow_timekeeper, &tk_core.timekeeper, sizeof(tk_core.timekeeper));

}



/**
@@ -2305,8 +2304,8 @@ static u64 logarithmic_accumulation(struct timekeeper *tk, u64 offset, 
 */

static bool timekeeping_advance(enum timekeeping_adv_mode mode)

{

	struct timekeeper *tk = &tk_core.shadow_timekeeper;

	struct timekeeper *real_tk = &tk_core.timekeeper;

	struct timekeeper *tk = &shadow_timekeeper;

	unsigned int clock_set = 0;

	int shift = 0, maxshift;

	u64 offset;