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timekeeping: Rework change_clocksource() to use shadow_timekeeper

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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: Anna-Maria Behnsen <anna-maria@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: John Stultz <jstultz@google.com>
Link: https://lore.kernel.org/all/20241009-devel-anna-maria-b4-timers-ptp-timekeeping-v2-18-554456a44a15@linutronix.de
This commit is contained in:
Anna-Maria Behnsen 2024-10-09 10:29:11 +02:00 committed by Thomas Gleixner
parent 82214756d3
commit 351619fc99
1 changed files with 7 additions and 11 deletions
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18
kernel/time/timekeeping.c
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@ -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);
scoped_guard (raw_spinlock_irqsave, &tk_core.lock) {
struct timekeeper *tks = &tk_core.shadow_timekeeper;
timekeeping_forward_now(tk);
old = tk->tkr_mono.clock;
tk_setup_internals(tk, new);
timekeeping_update(&tk_core, tk, TK_UPDATE_ALL | TK_MIRROR);
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)