From: Tony Lindgren <tony@atomide.com>
Date: Fri, 29 Sep 2006 07:45:10 +0000 (+0300)
Subject: ARM: OMAP: Avoid updating system time for sub-jiffy interrupts
X-Git-Tag: v2.6.18-omap1~25
X-Git-Url: http://pilppa.com/gitweb/?a=commitdiff_plain;h=afdf472d20737f91f098c6bc64f6170e8f739405;p=linux-2.6-omap-h63xx.git

ARM: OMAP: Avoid updating system time for sub-jiffy interrupts

Updating system time and reprogramming timer can cause latency
issues on busy systems with lots of interrupts with constant
updating of time and reprogramming the system timer.

If a non-timer dyntick interrupt happens within a jiffy from
the last interrupt, updating time and reprogramming the timer
is unnecessary as we will get a timer interrupt soon anyways.

Signed-off-by: Tony Lindgren <tony@atomide.com>
---

diff --git a/arch/arm/plat-omap/timer32k.c b/arch/arm/plat-omap/timer32k.c
index cf6df3378d3..27ee80d3244 100644
--- a/arch/arm/plat-omap/timer32k.c
+++ b/arch/arm/plat-omap/timer32k.c
@@ -221,6 +221,17 @@ static inline irqreturn_t _omap_32k_timer_interrupt(int irq, void *dev_id,
 static irqreturn_t omap_32k_timer_handler(int irq, void *dev_id,
 					struct pt_regs *regs)
 {
+	unsigned long now;
+
+	now = omap_32k_sync_timer_read();
+
+	/* Don't bother reprogramming timer if last tick was before next
+	 * jiffie. We will get another interrupt when previously programmed
+	 * timer expires. This cuts down interrupt load quite a bit.
+	 */
+	if (now - omap_32k_last_tick < OMAP_32K_TICKS_PER_HZ)
+		return IRQ_HANDLED;
+
 	return _omap_32k_timer_interrupt(irq, dev_id, regs);
 }