Messages in this thread Patch in this message | | | From | Anna-Maria Behnsen <> | Subject | [PATCH v6 13/21] timer: Retrieve next expiry of pinned/non-pinned timers separately | Date | Wed, 10 May 2023 09:28:09 +0200 |
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For the conversion of the NOHZ timer placement to a pull at expiry time model it's required to have separate expiry times for the pinned and the non-pinned (movable) timers. Therefore struct timer_events is introduced.
No functional change
Originally-by: Richard Cochran (linutronix GmbH) <richardcochran@gmail.com> Signed-off-by: Anna-Maria Behnsen <anna-maria@linutronix.de> Reviewed-by: Frederic Weisbecker <frederic@kernel.org> --- kernel/time/timer.c | 45 ++++++++++++++++++++++++++++++++++++++++----- 1 file changed, 40 insertions(+), 5 deletions(-)
diff --git a/kernel/time/timer.c b/kernel/time/timer.c index 010c8877fa85..e4b50760da3f 100644 --- a/kernel/time/timer.c +++ b/kernel/time/timer.c @@ -221,6 +221,11 @@ struct timer_base { static DEFINE_PER_CPU(struct timer_base, timer_bases[NR_BASES]); +struct timer_events { + u64 local; + u64 global; +}; + #ifdef CONFIG_NO_HZ_COMMON static DEFINE_STATIC_KEY_FALSE(timers_nohz_active); @@ -1997,17 +2002,17 @@ static void forward_base_clk(struct timer_base *base, unsigned long nextevt, */ u64 get_next_timer_interrupt(unsigned long basej, u64 basem) { + struct timer_events tevt = { .local = KTIME_MAX, .global = KTIME_MAX }; unsigned long nextevt, nextevt_local, nextevt_global; struct timer_base *base_local, *base_global; bool local_first, is_idle; - u64 expires = KTIME_MAX; /* * Pretend that there is no timer pending if the cpu is offline. * Possible pending timers will be migrated later to an active cpu. */ if (cpu_is_offline(smp_processor_id())) - return expires; + return tevt.local; base_local = this_cpu_ptr(&timer_bases[BASE_LOCAL]); base_global = this_cpu_ptr(&timer_bases[BASE_GLOBAL]); @@ -2052,16 +2057,46 @@ u64 get_next_timer_interrupt(unsigned long basej, u64 basem) /* We need to mark both bases in sync */ base_local->is_idle = base_global->is_idle = is_idle; - if (base_local->timers_pending || base_global->timers_pending) { + /* + * If the bases are not marked idle, i.e one of the events is at + * max. one tick away, then the CPU can't go into a NOHZ idle + * sleep. Use the earlier event of both and store it in the local + * expiry value. The next global event is irrelevant in this case + * and can be left as KTIME_MAX. CPU will wakeup on time. + */ + if (!is_idle) { /* If we missed a tick already, force 0 delta */ if (time_before(nextevt, basej)) nextevt = basej; - expires = basem + (u64)(nextevt - basej) * TICK_NSEC; + tevt.local = basem + (u64)(nextevt - basej) * TICK_NSEC; + goto unlock; } + + /* + * If the bases are marked idle, i.e. the next event on both the + * local and the global queue are farther away than a tick, + * evaluate both bases. No need to check whether one of the bases + * has an already expired timer as this is caught by the !is_idle + * condition above. + */ + if (base_local->timers_pending) + tevt.local = basem + (u64)(nextevt_local - basej) * TICK_NSEC; + + /* + * If the local queue expires first, then the global event can be + * ignored. The CPU wakes up before that. If the global queue is + * empty, nothing to do either. + */ + if (!local_first && base_global->timers_pending) + tevt.global = basem + (u64)(nextevt_global - basej) * TICK_NSEC; + +unlock: raw_spin_unlock(&base_global->lock); raw_spin_unlock(&base_local->lock); - return cmp_next_hrtimer_event(basem, expires); + tevt.local = min_t(u64, tevt.local, tevt.global); + + return cmp_next_hrtimer_event(basem, tevt.local); } /** -- 2.30.2
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