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

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Date:	Tue, 3 Oct 2006 20:36:20 -0700
From:	Andrew Morton <akpm@...l.org>
To:	Ingo Molnar <mingo@...e.hu>
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: Re: [patch] clockevents: drivers for i386, fix #2

On Tue, 3 Oct 2006 12:35:03 +0200
Ingo Molnar <mingo@...e.hu> wrote:

> 
> 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;
>  

Doesn't help.

> * 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.
> > 

Disabling IO_APIC doesn't fix the slowdown.

Disabling LOCAL_APIC does fix it.
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