Re: [PATCH v2 18/25] timekeeping: Rework change_clocksource() to use shadow_timekeeper

From: John Stultz
Date: Thu Oct 24 2024 - 17:59:16 EST


On Wed, Oct 9, 2024 at 1:29 AM Anna-Maria Behnsen
<anna-maria@xxxxxxxxxxxxx> wrote:
>
> From: Anna-Maria Behnsen <anna-maria@xxxxxxxxxxxxx>
>
> 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@xxxxxxxxxxxxx>
> ---
> kernel/time/timekeeping.c | 18 +++++++-----------
> 1 file changed, 7 insertions(+), 11 deletions(-)
>
> diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
> index 051041e92e54..6d21e9bf5c35 100644
> --- a/kernel/time/timekeeping.c
> +++ b/kernel/time/timekeeping.c
> @@ -1596,9 +1596,7 @@ 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.
> @@ -1614,16 +1612,14 @@ 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 *tk = &tk_core.shadow_timekeeper;

Same nit: tk_shadow maybe?

Acked-by: John Stultz <jstultz@xxxxxxxxxx>