linux-kernel - [PATCH 7/18] ARM: OMAP: Avoid updating system time for sub-jiffy interrupts

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Message-Id: <1176153771729-git-send-email-tony@atomide.com>
Date:	Mon,  9 Apr 2007 17:22:12 -0400
From:	Tony Lindgren <tony@...mide.com>
To:	linux-kernel@...r.kernel.org
Cc:	Tony Lindgren <tony@...mide.com>
Subject: [PATCH 7/18] 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@...mide.com>
---
 arch/arm/plat-omap/timer32k.c |   11 +++++++++++
 1 files changed, 11 insertions(+), 0 deletions(-)

--- a/arch/arm/plat-omap/timer32k.c
+++ b/arch/arm/plat-omap/timer32k.c
@@ -219,6 +219,17 @@ 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)
 {
+	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);
 }
 
-- 
1.4.4.2

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