Re: [PATCH v10a] timers: Move marking timer bases idle into tick_nohz_stop_tick()

Frederic Weisbecker
2024-02-20T11:41:59Z

Le Tue, Feb 20, 2024 at 11:48:19AM +0100, Anna-Maria Behnsen a écrit :
> Frederic Weisbecker <frederic@kernel.org> writes:
> diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
> index 01fb50c1b17e..b93f0e6f273f 100644
> --- a/kernel/time/tick-sched.c
> +++ b/kernel/time/tick-sched.c
> @@ -895,21 +895,6 @@ static void tick_nohz_stop_tick(struct tick_sched *ts, int cpu)
> /* Make sure we won't be trying to stop it twice in a row. */
> ts->timer_expires_base = 0;
>
> - /*
> - * If this CPU is the one which updates jiffies, then give up
> - * the assignment and let it be taken by the CPU which runs
> - * the tick timer next, which might be this CPU as well. If we
> - * don't drop this here, the jiffies might be stale and
> - * do_timer() never gets invoked. Keep track of the fact that it
> - * was the one which had the do_timer() duty last.
> - */
> - if (cpu == tick_do_timer_cpu) {
> - tick_do_timer_cpu = TICK_DO_TIMER_NONE;
> - ts->do_timer_last = 1;
> - } else if (tick_do_timer_cpu != TICK_DO_TIMER_NONE) {
> - ts->do_timer_last = 0;
> - }
> -
> /* Skip reprogram of event if it's not changed */
> if (ts->tick_stopped && (expires == ts->next_tick)) {
> /* Sanity check: make sure clockevent is actually programmed */

That should work but then you lose the optimization that resets
ts->do_timer_last even if the next timer hasn't changed.

Thanks.

> @@ -938,6 +923,21 @@ static void tick_nohz_stop_tick(struct tick_sched *ts, int cpu)
> trace_tick_stop(1, TICK_DEP_MASK_NONE);
> }
>
> + /*
> + * If this CPU is the one which updates jiffies, then give up
> + * the assignment and let it be taken by the CPU which runs
> + * the tick timer next, which might be this CPU as well. If we
> + * don't drop this here, the jiffies might be stale and
> + * do_timer() never gets invoked. Keep track of the fact that it
> + * was the one which had the do_timer() duty last.
> + */
> + if (cpu == tick_do_timer_cpu) {
> + tick_do_timer_cpu = TICK_DO_TIMER_NONE;
> + ts->do_timer_last = 1;
> + } else if (tick_do_timer_cpu != TICK_DO_TIMER_NONE) {
> + ts->do_timer_last = 0;
> + }
> +
> ts->next_tick = expires;
>
> /*