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Message-ID: <alpine.DEB.2.10.1406221417510.5170@nanos> Date: Sun, 22 Jun 2014 16:46:49 +0200 (CEST) From: Thomas Gleixner <tglx@...utronix.de> To: Stanislav Fomichev <stfomichev@...dex-team.ru> cc: john.stultz@...aro.org, prarit@...hat.com, paul.gortmaker@...driver.com, juri.lelli@...il.com, ddaney.cavm@...il.com, mbohan@...eaurora.org, david.vrabel@...rix.com, david.engraf@...go.com, linux-kernel@...r.kernel.org Subject: Re: [PATCH v2] hrtimers: calculate expires_next after all timers are executed On Wed, 19 Mar 2014, Stanislav Fomichev wrote: + * @next: time of the next event on this clock base What initializes that? It's 0 to begin with. > @@ -893,6 +895,10 @@ static int enqueue_hrtimer(struct hrtimer *timer, > */ > timer->state |= HRTIMER_STATE_ENQUEUED; > > + expires = ktime_sub(hrtimer_get_expires(timer), base->offset); This does not work when time gets set and the offset changes. We need to store the absolute expiry time and subtract the offset at evaluation time. > @@ -929,8 +935,10 @@ static void __remove_hrtimer(struct hrtimer *timer, > } > #endif > } > - if (!timerqueue_getnext(&base->active)) > + if (!timerqueue_getnext(&base->active)) { > base->cpu_base->active_bases &= ~(1 << base->index); > + base->next = ktime_set(KTIME_SEC_MAX, 0); > + } And what updates base->next if there are timers pending? > + for (i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++) { > + ktime_t expires; So this adds the third incarnation of finding the next expiring timer to the code. Not really helpful. Untested patch which addresses the issues below. Thanks, tglx --------------------> include/linux/hrtimer.h | 2 kernel/hrtimer.c | 162 ++++++++++++++++++++++++++---------------------- 2 files changed, 90 insertions(+), 74 deletions(-) Index: linux/include/linux/hrtimer.h =================================================================== --- linux.orig/include/linux/hrtimer.h +++ linux/include/linux/hrtimer.h @@ -141,6 +141,7 @@ struct hrtimer_sleeper { * @get_time: function to retrieve the current time of the clock * @softirq_time: the time when running the hrtimer queue in the softirq * @offset: offset of this clock to the monotonic base + * @expires_next: absolute time of the next event on this clock base */ struct hrtimer_clock_base { struct hrtimer_cpu_base *cpu_base; @@ -151,6 +152,7 @@ struct hrtimer_clock_base { ktime_t (*get_time)(void); ktime_t softirq_time; ktime_t offset; + ktime_t expires_next; }; enum hrtimer_base_type { Index: linux/kernel/hrtimer.c =================================================================== --- linux.orig/kernel/hrtimer.c +++ linux/kernel/hrtimer.c @@ -494,6 +494,36 @@ static inline void debug_deactivate(stru trace_hrtimer_cancel(timer); } +/* + * Find the next expiring timer and return the expiry in absolute + * CLOCK_MONOTONIC time. + */ +static ktime_t hrtimer_get_expires_next(struct hrtimer_cpu_base *cpu_base) +{ + ktime_t expires, expires_next = { .tv64 = KTIME_MAX }; + unsigned long idx, active = cpu_base->active_bases; + struct hrtimer_clock_base *base; + + while (active) { + idx = __ffs(active); + active &= ~(1UL << idx); + + base = cpu_base->clock_base + idx; + /* Adjust to CLOCK_MONOTONIC */ + expires = ktime_sub(base->expires_next, base->offset); + + if (expires.tv64 < expires_next.tv64) + expires_next = expires; + } + /* + * If clock_was_set() has changed base->offset the result + * might be negative. Fix it up to prevent a false positive in + * clockevents_program_event() + */ + expires.tv64 = 0; + return expires_next.tv64 < 0 ? expires : expires_next; +} + /* High resolution timer related functions */ #ifdef CONFIG_HIGH_RES_TIMERS @@ -542,32 +572,7 @@ static inline int hrtimer_hres_active(vo static void hrtimer_force_reprogram(struct hrtimer_cpu_base *cpu_base, int skip_equal) { - int i; - struct hrtimer_clock_base *base = cpu_base->clock_base; - ktime_t expires, expires_next; - - expires_next.tv64 = KTIME_MAX; - - for (i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++, base++) { - struct hrtimer *timer; - struct timerqueue_node *next; - - next = timerqueue_getnext(&base->active); - if (!next) - continue; - timer = container_of(next, struct hrtimer, node); - - expires = ktime_sub(hrtimer_get_expires(timer), base->offset); - /* - * clock_was_set() has changed base->offset so the - * result might be negative. Fix it up to prevent a - * false positive in clockevents_program_event() - */ - if (expires.tv64 < 0) - expires.tv64 = 0; - if (expires.tv64 < expires_next.tv64) - expires_next = expires; - } + ktime_t expires_next = hrtimer_get_expires_next(cpu_base); if (skip_equal && expires_next.tv64 == cpu_base->expires_next.tv64) return; @@ -891,6 +896,8 @@ EXPORT_SYMBOL_GPL(hrtimer_forward); static int enqueue_hrtimer(struct hrtimer *timer, struct hrtimer_clock_base *base) { + int leftmost; + debug_activate(timer); timerqueue_add(&base->active, &timer->node); @@ -902,7 +909,13 @@ static int enqueue_hrtimer(struct hrtime */ timer->state |= HRTIMER_STATE_ENQUEUED; - return (&timer->node == base->active.next); + leftmost = &timer->node == base->active.next; + /* + * If the new timer is the leftmost, update clock_base->expires_next. + */ + if (leftmost) + base->expires_next = hrtimer_get_expires(timer); + return leftmost; } /* @@ -919,27 +932,45 @@ static void __remove_hrtimer(struct hrti struct hrtimer_clock_base *base, unsigned long newstate, int reprogram) { - struct timerqueue_node *next_timer; + struct timerqueue_node *next; + struct hrtimer *next_timer; + bool first; + if (!(timer->state & HRTIMER_STATE_ENQUEUED)) goto out; - next_timer = timerqueue_getnext(&base->active); + /* + * If this is not the first timer of the clock base, we just + * remove it. No updates, no reprogramming. + */ + first = timerqueue_getnext(&base->active) == &timer->node; timerqueue_del(&base->active, &timer->node); - if (&timer->node == next_timer) { + if (!first) + goto out; + + /* + * Update cpu base and clock base. This needs to be done + * before calling into hrtimer_force_reprogram() as that + * relies on active_bases and expires_next. + */ + next = timerqueue_getnext(&base->active); + if (!next) { + base->cpu_base->active_bases &= ~(1 << base->index); + base->expires_next.tv64 = KTIME_MAX; + } else { + next_timer = container_of(next, struct hrtimer, node); + base->expires_next = hrtimer_get_expires(next_timer); + } + #ifdef CONFIG_HIGH_RES_TIMERS - /* Reprogram the clock event device. if enabled */ - if (reprogram && hrtimer_hres_active()) { - ktime_t expires; - - expires = ktime_sub(hrtimer_get_expires(timer), - base->offset); - if (base->cpu_base->expires_next.tv64 == expires.tv64) - hrtimer_force_reprogram(base->cpu_base, 1); - } -#endif + if (reprogram && hrtimer_hres_active()) { + ktime_t expires; + + expires = ktime_sub(hrtimer_get_expires(timer), base->offset); + if (base->cpu_base->expires_next.tv64 == expires.tv64) + hrtimer_force_reprogram(base->cpu_base, 1); } - if (!timerqueue_getnext(&base->active)) - base->cpu_base->active_bases &= ~(1 << base->index); +#endif out: timer->state = newstate; } @@ -1154,35 +1185,21 @@ EXPORT_SYMBOL_GPL(hrtimer_get_remaining) ktime_t hrtimer_get_next_event(void) { struct hrtimer_cpu_base *cpu_base = &__get_cpu_var(hrtimer_bases); - struct hrtimer_clock_base *base = cpu_base->clock_base; - ktime_t delta, mindelta = { .tv64 = KTIME_MAX }; + ktime_t next, delta = { .tv64 = KTIME_MAX }; unsigned long flags; - int i; raw_spin_lock_irqsave(&cpu_base->lock, flags); if (!hrtimer_hres_active()) { - for (i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++, base++) { - struct hrtimer *timer; - struct timerqueue_node *next; - - next = timerqueue_getnext(&base->active); - if (!next) - continue; - - timer = container_of(next, struct hrtimer, node); - delta.tv64 = hrtimer_get_expires_tv64(timer); - delta = ktime_sub(delta, base->get_time()); - if (delta.tv64 < mindelta.tv64) - mindelta.tv64 = delta.tv64; - } + next = hrtimer_get_expires_next(cpu_base); + delta = ktime_sub(next, ktime_get()); + if (delta.tv64 < 0) + delta.tv64 = 0; } raw_spin_unlock_irqrestore(&cpu_base->lock, flags); - if (mindelta.tv64 < 0) - mindelta.tv64 = 0; - return mindelta; + return delta; } #endif @@ -1292,6 +1309,7 @@ static void __run_hrtimer(struct hrtimer */ void hrtimer_interrupt(struct clock_event_device *dev) { + struct hrtimer_clock_base *base; struct hrtimer_cpu_base *cpu_base = &__get_cpu_var(hrtimer_bases); ktime_t expires_next, now, entry_time, delta; int i, retries = 0; @@ -1303,7 +1321,6 @@ void hrtimer_interrupt(struct clock_even raw_spin_lock(&cpu_base->lock); entry_time = now = hrtimer_update_base(cpu_base); retry: - expires_next.tv64 = KTIME_MAX; /* * We set expires_next to KTIME_MAX here with cpu_base->lock * held to prevent that a timer is enqueued in our queue via @@ -1314,7 +1331,6 @@ retry: cpu_base->expires_next.tv64 = KTIME_MAX; for (i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++) { - struct hrtimer_clock_base *base; struct timerqueue_node *node; ktime_t basenow; @@ -1342,23 +1358,20 @@ retry: * timer will have to trigger a wakeup anyway. */ - if (basenow.tv64 < hrtimer_get_softexpires_tv64(timer)) { - ktime_t expires; - - expires = ktime_sub(hrtimer_get_expires(timer), - base->offset); - if (expires.tv64 < 0) - expires.tv64 = KTIME_MAX; - if (expires.tv64 < expires_next.tv64) - expires_next = expires; + if (basenow.tv64 < hrtimer_get_softexpires_tv64(timer)) break; - } __run_hrtimer(timer, &basenow); } } /* + * We might have dropped cpu_base->lock and the callbacks + * might have added timers. Find the timer which expires first. + */ + expires_next = hrtimer_get_expires_next(cpu_base); + + /* * Store the new expiry value so the migration code can verify * against it. */ @@ -1678,6 +1691,7 @@ static void init_hrtimers_cpu(int cpu) for (i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++) { cpu_base->clock_base[i].cpu_base = cpu_base; timerqueue_init_head(&cpu_base->clock_base[i].active); + cpu_base->clock_base[i].expires_next.tv64 = KTIME_MAX; } hrtimer_init_hres(cpu_base); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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