linux-kernel - [PATCH V2 2/2] hrtimer: use __ffs() to iterate over valid bits from active

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Message-Id: <aa0ab84ff46cdc4a2d7aef475b2c032009f23d29.1395897612.git.viresh.kumar@linaro.org>
Date:	Thu, 27 Mar 2014 10:53:37 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	tglx@...utronix.de
Cc:	linaro-kernel@...ts.linaro.org, linux-kernel@...r.kernel.org,
	fweisbec@...il.com, linaro-networking@...aro.org,
	Viresh Kumar <viresh.kumar@...aro.org>
Subject: [PATCH V2 2/2] hrtimer: use __ffs() to iterate over valid bits from active_bases

Currently we are iterating over all possible (currently four) bits of
active_bases to see if corresponding clock bases are active. This is good enough
for cases where 3 or 4 bases are used but if only 1 or 2 are used then it makes
more sense to use __ffs() to find the right bit directly.

Suggested-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
---
V1->V2: Instead of removing active_bases use __ffs() on it to make loop more
efficient.

I tried to use for_each_set_bit() first and then it looked overdone. And so used
a simple form, __ffs() with some code to clear bits.

 kernel/hrtimer.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index acfef5f..ea90228 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -1265,6 +1265,7 @@ void hrtimer_interrupt(struct clock_event_device *dev)
 {
 	struct hrtimer_cpu_base *cpu_base = &__get_cpu_var(hrtimer_bases);
 	ktime_t expires_next, now, entry_time, delta;
+	unsigned long active_bases = cpu_base->active_bases;
 	int i, retries = 0;
 
 	BUG_ON(!cpu_base->hres_active);
@@ -1284,15 +1285,11 @@ retry:
 	 */
 	cpu_base->expires_next.tv64 = KTIME_MAX;
 
-	for (i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++) {
-		struct hrtimer_clock_base *base;
+	while ((i = __ffs(active_bases))) {
+		struct hrtimer_clock_base *base = cpu_base->clock_base + i;
 		struct timerqueue_node *node;
 		ktime_t basenow;
 
-		if (!(cpu_base->active_bases & (1 << i)))
-			continue;
-
-		base = cpu_base->clock_base + i;
 		basenow = ktime_add(now, base->offset);
 
 		while ((node = timerqueue_getnext(&base->active))) {
@@ -1327,6 +1324,8 @@ retry:
 
 			__run_hrtimer(timer, &basenow);
 		}
+
+		active_bases &= ~(1 << i);
 	}
 
 	/*
-- 
1.7.12.rc2.18.g61b472e

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