linux-kernel - [patch] clockevents: drivers for i386, fix #2

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Message-ID: <20061003103503.GA6350@elte.hu>
Date:	Tue, 3 Oct 2006 12:35:03 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Andrew Morton <akpm@...l.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>, Jim Gettys <jg@...top.org>,
	John Stultz <johnstul@...ibm.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Dave Jones <davej@...hat.com>
Subject: [patch] clockevents: drivers for i386, fix #2


* Ingo Molnar <mingo@...e.hu> wrote:

> yeah, i suspect it works again if you disable:
> 
>  CONFIG_X86_UP_APIC=y
>  CONFIG_X86_UP_IOAPIC=y
>  CONFIG_X86_LOCAL_APIC=y
>  CONFIG_X86_IO_APIC=y
> 
> as the slowdown has the feeling of a runaway lapic timer irq.
> 
> from code review so far we can only see an udelay(10) difference in 
> the initialization sequence of the PIT - we'll send a fix for that but 
> i dont think that's the cause of the bug.

the patch below fixes that particular bug. But ... the symptoms you are 
describing have the feeling of being apic related.

	Ingo

-------------------->
Subject: clockevents: drivers for i386, fix #2
From: Ingo Molnar <mingo@...e.hu>

add back a mistakenly removed udelay(10) to the PIT initialization
sequence.

Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 arch/i386/kernel/i8253.c |    1 +
 1 file changed, 1 insertion(+)

Index: linux/arch/i386/kernel/i8253.c
===================================================================
--- linux.orig/arch/i386/kernel/i8253.c
+++ linux/arch/i386/kernel/i8253.c
@@ -45,6 +45,7 @@ static void init_pit_timer(enum clock_ev
 		outb_p(0x34, PIT_MODE);
 		udelay(10);
 		outb_p(LATCH & 0xff , PIT_CH0);	/* LSB */
+		udelay(10);
 		outb(LATCH >> 8 , PIT_CH0);	/* MSB */
 		break;
 
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