Messages in this thread Patch in this message | | | From | Anna-Maria Behnsen <> | Subject | [PATCH v4 04/16] timer: Rework idle logic | Date | Fri, 4 Nov 2022 15:57:25 +0100 |
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From: Thomas Gleixner <tglx@linutronix.de>
To improve readability of the code, split base->idle calculation and expires calculation into separate parts.
Thereby the following subtle change happens if the next event is just one jiffy ahead and the tick was already stopped: Originally base->is_idle remains true in this situation. Now base->is_idle turns to false. This may spare an IPI if a timer is enqueued remotely to an idle CPU that is going to tick on the next jiffy.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Anna-Maria Behnsen <anna-maria@linutronix.de> Reviewed-by: Frederic Weisbecker <frederic@kernel.org> --- v4: Change condition to force 0 delta and update commit message (Frederic) --- kernel/time/timer.c | 29 ++++++++++++++--------------- 1 file changed, 14 insertions(+), 15 deletions(-)
diff --git a/kernel/time/timer.c b/kernel/time/timer.c index 4547d2efcb86..0e9f609f5a38 100644 --- a/kernel/time/timer.c +++ b/kernel/time/timer.c @@ -1727,21 +1727,20 @@ u64 get_next_timer_interrupt(unsigned long basej, u64 basem) base->clk = nextevt; } - if (time_before_eq(nextevt, basej)) { - expires = basem; - base->is_idle = false; - } else { - if (base->timers_pending) - expires = basem + (u64)(nextevt - basej) * TICK_NSEC; - /* - * If we expect to sleep more than a tick, mark the base idle. - * Also the tick is stopped so any added timer must forward - * the base clk itself to keep granularity small. This idle - * logic is only maintained for the BASE_STD base, deferrable - * timers may still see large granularity skew (by design). - */ - if ((expires - basem) > TICK_NSEC) - base->is_idle = true; + /* + * Base is idle if the next event is more than a tick away. Also + * the tick is stopped so any added timer must forward the base clk + * itself to keep granularity small. This idle logic is only + * maintained for the BASE_STD base, deferrable timers may still + * see large granularity skew (by design). + */ + base->is_idle = time_after(nextevt, basej + 1); + + if (base->timers_pending) { + /* If we missed a tick already, force 0 delta */ + if (time_before(nextevt, basej)) + nextevt = basej; + expires = basem + (u64)(nextevt - basej) * TICK_NSEC; } raw_spin_unlock(&base->lock); -- 2.30.2
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