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From: Frederic Weisbecker <frederic@kernel.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>,
	Frederic Weisbecker <frederic@kernel.org>,
	Anna-Maria Gleixner <anna-maria@linutronix.de>,
	Peter Zijlstra <peterz@infradead.org>,
	Juri Lelli <juri.lelli@redhat.com>
Subject: [PATCH 8/9] timer: Remove must_forward_clk
Date: Tue,  7 Jul 2020 03:32:52 +0200	[thread overview]
Message-ID: <20200707013253.26770-9-frederic@kernel.org> (raw)
In-Reply-To: <20200707013253.26770-1-frederic@kernel.org>

There is no reason to keep this guard around. The code makes sure that
base->clk remains sane and won't be forwarded beyond jiffies nor set
backward.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Anna-Maria Gleixner <anna-maria@linutronix.de>
Cc: Juri Lelli <juri.lelli@redhat.com>
---
 kernel/time/timer.c | 22 ++++++----------------
 1 file changed, 6 insertions(+), 16 deletions(-)

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index cbc5ac7f772d..60126d5c79e1 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -205,7 +205,6 @@ struct timer_base {
 	unsigned long		next_expiry;
 	unsigned int		cpu;
 	bool			is_idle;
-	bool			must_forward_clk;
 	DECLARE_BITMAP(pending_map, WHEEL_SIZE);
 	struct hlist_head	vectors[WHEEL_SIZE];
 } ____cacheline_aligned;
@@ -885,12 +884,13 @@ get_target_base(struct timer_base *base, unsigned tflags)
 
 static inline void forward_timer_base(struct timer_base *base)
 {
-	unsigned long jnow;
+	unsigned long jnow = READ_ONCE(jiffies);
 
-	if (!base->must_forward_clk)
-		return;
-
-	jnow = READ_ONCE(jiffies);
+	/*
+	 * No need to forward if we are close enough below jiffies.
+	 * Also while executing timers, base->clk is 1 offset ahead
+	 * of jiffies to avoid endless requeuing to current jffies.
+	 */
 	if ((long)(jnow - base->clk) < 2)
 		return;
 
@@ -1721,16 +1721,8 @@ static inline void __run_timers(struct timer_base *base)
 	timer_base_lock_expiry(base);
 	raw_spin_lock_irq(&base->lock);
 
-	/*
-	 * timer_base::must_forward_clk must be cleared before running
-	 * timers so that any timer functions that call mod_timer() will
-	 * not try to forward the base.
-	 */
-	base->must_forward_clk = false;
-
 	while (time_after_eq(jiffies, base->clk) &&
 	       time_after_eq(jiffies, base->next_expiry)) {
-
 		levels = collect_expired_timers(base, heads);
 		base->clk++;
 		base->next_expiry = __next_timer_interrupt(base);
@@ -1738,7 +1730,6 @@ static inline void __run_timers(struct timer_base *base)
 		while (levels--)
 			expire_timers(base, heads + levels);
 	}
-	base->must_forward_clk = true;
 	raw_spin_unlock_irq(&base->lock);
 	timer_base_unlock_expiry(base);
 }
@@ -1934,7 +1925,6 @@ int timers_prepare_cpu(unsigned int cpu)
 		base->clk = jiffies;
 		base->next_expiry = base->clk + NEXT_TIMER_MAX_DELTA;
 		base->is_idle = false;
-		base->must_forward_clk = true;
 	}
 	return 0;
 }
-- 
2.26.2


  parent reply	other threads:[~2020-07-07  1:33 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-07  1:32 [PATCH 0/9] timer: Reduce timers softirq v2 Frederic Weisbecker
2020-07-07  1:32 ` [PATCH 1/9] timer: Move trigger_dyntick_cpu() to enqueue_timer() Frederic Weisbecker
2020-07-09 12:17   ` Anna-Maria Behnsen
2020-07-15 13:20     ` Frederic Weisbecker
2020-07-07  1:32 ` [PATCH 2/9] timer: Add comments about calc_index() ceiling work Frederic Weisbecker
2020-07-14  9:13   ` Thomas Gleixner
2020-07-17 12:55     ` Frederic Weisbecker
2020-07-07  1:32 ` [PATCH 3/9] timer: Optimize _next_timer_interrupt() level iteration Frederic Weisbecker
2020-07-07  1:32 ` [PATCH 4/9] timers: Always keep track of next expiry Frederic Weisbecker
2020-07-14  8:49   ` Anna-Maria Behnsen
2020-07-17 12:51     ` Frederic Weisbecker
2020-07-07  1:32 ` [PATCH 5/9] timer: Reuse next expiry cache after nohz exit Frederic Weisbecker
2020-07-07  1:32 ` [PATCH 6/9] timer: Expand clk forward logic beyond nohz Frederic Weisbecker
2020-07-07  1:32 ` [PATCH 7/9] timer: Spare timer softirq until next expiry Frederic Weisbecker
2020-07-07  1:32 ` Frederic Weisbecker [this message]
2020-07-07  1:32 ` [PATCH 9/9] timer: Lower base clock forwarding threshold Frederic Weisbecker
2020-07-09  7:02 ` [PATCH 0/9] timer: Reduce timers softirq v2 Juri Lelli

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