linux-kernel - [PATCH v4 21/36] hrtimer: Make remote enqueue decision less restrictive

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Message-Id: <20171221104205.7269-22-anna-maria@linutronix.de>
Date:   Thu, 21 Dec 2017 11:41:50 +0100
From:   Anna-Maria Gleixner <anna-maria@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, keescook@...omium.org,
        Christoph Hellwig <hch@....de>,
        John Stultz <john.stultz@...aro.org>,
        Anna-Maria Gleixner <anna-maria@...utronix.de>
Subject: [PATCH v4 21/36] hrtimer: Make remote enqueue decision less restrictive

The current decision whether a timer can be queued on a remote CPU checks
for timer->expiry <= remote_cpu_base.expires_next.

This is too restrictive because a timer with the same expiry time as an
existing timer will be enqueued on right-hand size of the existing timer
inside the rbtree, i.e. behind the first expiring timer.

So its safe to allow enqueuing timers with the same expiry time as the
first expiring timer on a remote CPU base.

Signed-off-by: Anna-Maria Gleixner <anna-maria@...utronix.de>
---
 kernel/time/hrtimer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index c8528b932247..a1c92615ac07 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -168,7 +168,7 @@ hrtimer_check_target(struct hrtimer *timer, struct hrtimer_clock_base *new_base)
 	ktime_t expires;
 
 	expires = ktime_sub(hrtimer_get_expires(timer), new_base->offset);
-	return expires <= new_base->cpu_base->expires_next;
+	return expires < new_base->cpu_base->expires_next;
 }
 
 static inline
-- 
2.11.0