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    Subject[PATCH v8 03/25] timer: Do not IPI for deferrable timers
    Date
    Deferrable timers do not prevent CPU from going idle and are not taken into
    account on idle path. Sending an IPI to a remote CPU when a new first
    deferrable timer was enqueued will wake up the remote CPU and but nothing
    will be done regarding the deferrable timers.

    Drop IPI completely when a new first deferrable timer was enqueued.

    Signed-off-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
    Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
    ---
    v8: Update comment

    v6: new patch
    ---
    kernel/time/timer.c | 15 ++++++---------
    1 file changed, 6 insertions(+), 9 deletions(-)

    diff --git a/kernel/time/timer.c b/kernel/time/timer.c
    index 63a8ce7177dd..7d06351aff54 100644
    --- a/kernel/time/timer.c
    +++ b/kernel/time/timer.c
    @@ -571,18 +571,15 @@ static int calc_wheel_index(unsigned long expires, unsigned long clk,
    static void
    trigger_dyntick_cpu(struct timer_base *base, struct timer_list *timer)
    {
    - if (!is_timers_nohz_active())
    - return;
    -
    /*
    - * TODO: This wants some optimizing similar to the code below, but we
    - * will do that when we switch from push to pull for deferrable timers.
    + * Deferrable timers do not prevent CPU from entering dynticks and are
    + * not taken into account on idle/nohz_full path. An IPI when a new
    + * deferrable timer is enqueued will wake up the remote CPU but nothing
    + * will be done with the deferrable timer base. Therefore skip remote
    + * IPI for deferrable timers completely.
    */
    - if (timer->flags & TIMER_DEFERRABLE) {
    - if (tick_nohz_full_cpu(base->cpu))
    - wake_up_nohz_cpu(base->cpu);
    + if (!is_timers_nohz_active() || timer->flags & TIMER_DEFERRABLE)
    return;
    - }

    /*
    * We might have to IPI the remote CPU if the base is idle and the
    --
    2.39.2
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