linux-kernel - [PATCH] hrtimers: conditionally lock/unlock spinlock in hrtimer_get_next

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Message-Id: <1402305825-3015-1-git-send-email-stfomichev@yandex-team.ru>
Date:	Mon,  9 Jun 2014 13:23:45 +0400
From:	Stanislav Fomichev <stfomichev@...dex-team.ru>
To:	tglx@...utronix.de, stfomichev@...dex-team.ru,
	viresh.kumar@...aro.org, paul.gortmaker@...driver.com,
	peterz@...radead.org, stuart.w.hayes@...il.com,
	david.vrabel@...rix.com
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH] hrtimers: conditionally lock/unlock spinlock in hrtimer_get_next_event

In hrtimer_get_next_event we unconditionally lock/unlock spinlock, even if it's
not required (hrtimer_hres_active() != 0). This patch moves
locking/unlocking and mindelta range check inside the if clause,
so we don't execute unnecessary operations.

Signed-off-by: Stanislav Fomichev <stfomichev@...dex-team.ru>
---
 kernel/hrtimer.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index 39f339dcbe93..ce21e5f6bcf0 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -1166,9 +1166,9 @@ ktime_t hrtimer_get_next_event(void)
 	unsigned long flags;
 	int i;
 
-	raw_spin_lock_irqsave(&cpu_base->lock, flags);
-
 	if (!hrtimer_hres_active()) {
+		raw_spin_lock_irqsave(&cpu_base->lock, flags);
+
 		for (i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++, base++) {
 			struct hrtimer *timer;
 			struct timerqueue_node *next;
@@ -1183,12 +1183,13 @@ ktime_t hrtimer_get_next_event(void)
 			if (delta.tv64 < mindelta.tv64)
 				mindelta.tv64 = delta.tv64;
 		}
-	}
 
-	raw_spin_unlock_irqrestore(&cpu_base->lock, flags);
+		raw_spin_unlock_irqrestore(&cpu_base->lock, flags);
+
+		if (mindelta.tv64 < 0)
+			mindelta.tv64 = 0;
+	}
 
-	if (mindelta.tv64 < 0)
-		mindelta.tv64 = 0;
 	return mindelta;
 }
 #endif
-- 
1.8.3.2

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