90 lines
3.3 KiB
Diff
90 lines
3.3 KiB
Diff
From: Anna-Maria Gleixner <anna-maria@linutronix.de>
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Date: Sun, 22 Oct 2017 23:39:57 +0200
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Subject: [PATCH 19/36] hrtimer: Unify handling of hrtimer remove
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Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.14/older/patches-4.14-rt1.tar.xz
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When the first hrtimer on the current CPU is removed,
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hrtimer_force_reprogram() is invoked but only when
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CONFIG_HIGH_RES_TIMERS=y and hrtimer_cpu_base.hres_active is set.
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hrtimer_force_reprogram() updates hrtimer_cpu_base.expires_next and
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reprograms the clock event device. When CONFIG_HIGH_RES_TIMERS=y and
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hrtimer_cpu_base.hres_active is set, a pointless hrtimer interrupt can be
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prevented.
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hrtimer_check_target() makes the 'can remote enqueue' decision. As soon as
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hrtimer_check_target() is unconditionally available and
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hrtimer_cpu_base.expires_next is updated by hrtimer_reprogram(),
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hrtimer_force_reprogram() needs to be available unconditionally as well to
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prevent the following scenario with CONFIG_HIGH_RES_TIMERS=n:
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- the first hrtimer on this CPU is removed and hrtimer_force_reprogram() is
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not executed
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- CPU goes idle (next timer is calculated and hrtimers are taken into
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account)
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- a hrtimer is enqueued remote on the idle CPU: hrtimer_check_target()
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compares expiry value and hrtimer_cpu_base.expires_next. The expiry value
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is after expires_next, so the hrtimer is enqueued. This timer will fire
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late, if it expires before the effective first hrtimer on this CPU and
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the comparison was with an outdated expires_next value.
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To prevent this scenario, make hrtimer_force_reprogram() unconditional
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except the effective reprogramming part, which gets eliminated by the
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compiler in the CONFIG_HIGH_RES_TIMERS=n case.
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Signed-off-by: Anna-Maria Gleixner <anna-maria@linutronix.de>
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Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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---
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kernel/time/hrtimer.c | 10 ++++------
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1 file changed, 4 insertions(+), 6 deletions(-)
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--- a/kernel/time/hrtimer.c
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+++ b/kernel/time/hrtimer.c
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@@ -523,9 +523,6 @@ hrtimer_force_reprogram(struct hrtimer_c
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{
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ktime_t expires_next;
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- if (!__hrtimer_hres_active(cpu_base))
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- return;
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-
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expires_next = __hrtimer_get_next_event(cpu_base);
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if (skip_equal && expires_next == cpu_base->expires_next)
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@@ -534,6 +531,9 @@ hrtimer_force_reprogram(struct hrtimer_c
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cpu_base->expires_next = expires_next;
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/*
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+ * If hres is not active, hardware does not have to be
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+ * reprogrammed yet.
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+ *
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* If a hang was detected in the last timer interrupt then we
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* leave the hang delay active in the hardware. We want the
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* system to make progress. That also prevents the following
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@@ -547,7 +547,7 @@ hrtimer_force_reprogram(struct hrtimer_c
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* set. So we'd effectivly block all timers until the T2 event
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* fires.
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*/
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- if (cpu_base->hang_detected)
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+ if (!__hrtimer_hres_active(cpu_base) || cpu_base->hang_detected)
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return;
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tick_program_event(cpu_base->expires_next, 1);
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@@ -848,7 +848,6 @@ static void __remove_hrtimer(struct hrti
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if (!timerqueue_del(&base->active, &timer->node))
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cpu_base->active_bases &= ~(1 << base->index);
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-#ifdef CONFIG_HIGH_RES_TIMERS
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/*
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* Note: If reprogram is false we do not update
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* cpu_base->next_timer. This happens when we remove the first
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@@ -859,7 +858,6 @@ static void __remove_hrtimer(struct hrti
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*/
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if (reprogram && timer == cpu_base->next_timer)
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hrtimer_force_reprogram(cpu_base, 1);
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-#endif
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}
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/*
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