Commit 351619fc authored by Anna-Maria Behnsen's avatar Anna-Maria Behnsen Committed by Thomas Gleixner
Browse files

timekeeping: Rework change_clocksource() to use shadow_timekeeper 



Updates of the timekeeper can be done by operating on the shadow timekeeper
and afterwards copying the result into the real timekeeper. This has the
advantage, that the sequence count write protected region is kept as small
as possible.

Convert change_clocksource() to use this scheme.

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-v2-18-554456a44a15@linutronix.de
parent 82214756

kernel/time/timekeeping.c

+7 −11
Original line number Diff line number Diff line
@@ -1627,9 +1627,7 @@ static void __timekeeping_set_tai_offset(struct timekeeper *tk, s32 tai_offset) 
 */

static int change_clocksource(void *data)

{

	struct timekeeper *tk = &tk_core.timekeeper;

	struct clocksource *new = data, *old = NULL;

	unsigned long flags;



	/*

	 * If the clocksource is in a module, get a module reference.
@@ -1645,16 +1643,14 @@ static int change_clocksource(void *data) 
		return 0;

	}



	raw_spin_lock_irqsave(&tk_core.lock, flags);

	write_seqcount_begin(&tk_core.seq);



	timekeeping_forward_now(tk);

	old = tk->tkr_mono.clock;

	tk_setup_internals(tk, new);

	timekeeping_update(&tk_core, tk, TK_UPDATE_ALL | TK_MIRROR);

	scoped_guard (raw_spinlock_irqsave, &tk_core.lock) {

		struct timekeeper *tks = &tk_core.shadow_timekeeper;



	write_seqcount_end(&tk_core.seq);

	raw_spin_unlock_irqrestore(&tk_core.lock, flags);

		timekeeping_forward_now(tks);

		old = tks->tkr_mono.clock;

		tk_setup_internals(tks, new);

		timekeeping_update_from_shadow(&tk_core, TK_UPDATE_ALL);

	}



	if (old) {

		if (old->disable)