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Wysocki" , Arjan van de Ven , "Paul E . McKenney" , Frederic Weisbecker , Rik van Riel , Anna-Maria Behnsen , Richard Cochran Subject: [PATCH v4 07/16] timer: Retrieve next expiry of pinned/non-pinned timers seperately Date: Fri, 4 Nov 2022 15:57:28 +0100 Message-Id: <20221104145737.71236-8-anna-maria@linutronix.de> In-Reply-To: <20221104145737.71236-1-anna-maria@linutronix.de> References: <20221104145737.71236-1-anna-maria@linutronix.de> MIME-Version: 1.0 X-Spam-Status: No, score=-4.4 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_MED,SPF_HELO_NONE, SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1748578079981147594?= X-GMAIL-MSGID: =?utf-8?q?1748578079981147594?= For the conversion of the NOHZ timer placement to a pull at expiry time model it's required to have seperate 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) Signed-off-by: Anna-Maria Behnsen Reviewed-by: Frederic Weisbecker --- kernel/time/tick-internal.h | 8 ++++- kernel/time/tick-sched.c | 20 ++++++++---- kernel/time/timer.c | 65 ++++++++++++++++++++++++++++--------- 3 files changed, 70 insertions(+), 23 deletions(-) diff --git a/kernel/time/tick-internal.h b/kernel/time/tick-internal.h index 649f2b48e8f0..fcb2d45c2934 100644 --- a/kernel/time/tick-internal.h +++ b/kernel/time/tick-internal.h @@ -8,6 +8,11 @@ #include "timekeeping.h" #include "tick-sched.h" +struct timer_events { + u64 local; + u64 global; +}; + #ifdef CONFIG_GENERIC_CLOCKEVENTS # define TICK_DO_TIMER_NONE -1 @@ -163,7 +168,8 @@ static inline void timers_update_nohz(void) { } DECLARE_PER_CPU(struct hrtimer_cpu_base, hrtimer_bases); -extern u64 get_next_timer_interrupt(unsigned long basej, u64 basem); +extern void get_next_timer_interrupt(unsigned long basej, u64 basem, + struct timer_events *tevt); void timer_clear_idle(void); #define CLOCK_SET_WALL \ diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index 7ffdc7ba19b4..78f172d1f3d2 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -784,7 +784,8 @@ static inline bool local_timer_softirq_pending(void) static ktime_t tick_nohz_next_event(struct tick_sched *ts, int cpu) { - u64 basemono, next_tick, delta, expires; + struct timer_events tevt = { .local = KTIME_MAX, .global = KTIME_MAX }; + u64 basemono, delta, expires; unsigned long basejiff; unsigned int seq; @@ -809,7 +810,11 @@ static ktime_t tick_nohz_next_event(struct tick_sched *ts, int cpu) */ if (rcu_needs_cpu() || arch_needs_cpu() || irq_work_needs_cpu() || local_timer_softirq_pending()) { - next_tick = basemono + TICK_NSEC; + /* + * If anyone needs the CPU, treat this as a local + * timer expiring in a jiffy. + */ + tevt.local = basemono + TICK_NSEC; } else { /* * Get the next pending timer. If high resolution @@ -818,17 +823,18 @@ static ktime_t tick_nohz_next_event(struct tick_sched *ts, int cpu) * disabled this also looks at the next expiring * hrtimer. */ - next_tick = get_next_timer_interrupt(basejiff, basemono); - ts->next_timer = next_tick; + get_next_timer_interrupt(basejiff, basemono, &tevt); + tevt.local = min_t(u64, tevt.local, tevt.global); + ts->next_timer = tevt.local; } /* * If the tick is due in the next period, keep it ticking or * force prod the timer. */ - WARN_ON_ONCE(basemono > next_tick); + WARN_ON_ONCE(basemono > tevt.local); - delta = next_tick - basemono; + delta = tevt.local - basemono; if (delta <= (u64)TICK_NSEC) { /* * Tell the timer code that the base is not idle, i.e. undo @@ -861,7 +867,7 @@ static ktime_t tick_nohz_next_event(struct tick_sched *ts, int cpu) else expires = KTIME_MAX; - ts->timer_expires = min_t(u64, expires, next_tick); + ts->timer_expires = min_t(u64, expires, tevt.local); out: return ts->timer_expires; diff --git a/kernel/time/timer.c b/kernel/time/timer.c index 0e2abd906916..d272672935da 100644 --- a/kernel/time/timer.c +++ b/kernel/time/timer.c @@ -1664,7 +1664,7 @@ static void next_expiry_recalc(struct timer_base *base) * Check, if the next hrtimer event is before the next timer wheel * event: */ -static u64 cmp_next_hrtimer_event(u64 basem, u64 expires) +static void cmp_next_hrtimer_event(u64 basem, struct timer_events *tevt) { u64 nextevt = hrtimer_get_next_event(); @@ -1672,15 +1672,17 @@ static u64 cmp_next_hrtimer_event(u64 basem, u64 expires) * If high resolution timers are enabled * hrtimer_get_next_event() returns KTIME_MAX. */ - if (expires <= nextevt) - return expires; + if (tevt->local <= nextevt) + return; /* * If the next timer is already expired, return the tick base * time so the tick is fired immediately. */ - if (nextevt <= basem) - return basem; + if (nextevt <= basem) { + tevt->local = basem; + return; + } /* * Round up to the next jiffie. High resolution timers are @@ -1690,7 +1692,7 @@ static u64 cmp_next_hrtimer_event(u64 basem, u64 expires) * * Use DIV_ROUND_UP_ULL to prevent gcc calling __divdi3 */ - return DIV_ROUND_UP_ULL(nextevt, TICK_NSEC) * TICK_NSEC; + tevt->local = DIV_ROUND_UP_ULL(nextevt, TICK_NSEC) * TICK_NSEC; } @@ -1718,26 +1720,31 @@ static void forward_base_clk(struct timer_base *base, unsigned long nextevt, } /** - * get_next_timer_interrupt - return the time (clock mono) of the next timer + * get_next_timer_interrupt * @basej: base time jiffies * @basem: base time clock monotonic + * @tevt: Pointer to the storage for the expiry values * - * Returns the tick aligned clock monotonic time of the next pending - * timer or KTIME_MAX if no timer is pending. + * Stores the next pending local and global timer expiry values in the + * struct pointed to by @tevt. If a queue is empty the corresponding field + * is set to KTIME_MAX. */ -u64 get_next_timer_interrupt(unsigned long basej, u64 basem) +void get_next_timer_interrupt(unsigned long basej, u64 basem, + struct timer_events *tevt) { unsigned long nextevt, nextevt_local, nextevt_global; struct timer_base *base_local, *base_global; bool local_first, is_idle; - u64 expires = KTIME_MAX; + + /* Preset local / global events */ + tevt->local = tevt->global = 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; base_local = this_cpu_ptr(&timer_bases[BASE_LOCAL]); base_global = this_cpu_ptr(&timer_bases[BASE_GLOBAL]); @@ -1782,16 +1789,44 @@ 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); + cmp_next_hrtimer_event(basem, tevt); } /**