linux-kernel - Re: [PATCH] x86: apic

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Date:	Fri, 10 Oct 2008 20:31:01 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	"Maciej W. Rozycki" <macro@...ux-mips.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: apic - unify APIC_DIVISOR

[Pallipadi, Venkatesh - Fri, Oct 10, 2008 at 09:11:06AM -0700]
| 
| 
| >-----Original Message-----
| >From: Cyrill Gorcunov [mailto:gorcunov@...il.com]
| >Sent: Friday, October 10, 2008 8:00 AM
| >To: Ingo Molnar; Maciej W. Rozycki
| >Cc: LKML; Pallipadi, Venkatesh
| >Subject: [PATCH] x86: apic - unify APIC_DIVISOR
| >
| >Use APIC_DIVISOR being set to 16 for both 32/64bit
| >mode. To escape APIC timer underflow during calibration
| >set it to the maximum possible value.
| >
| >Also typo error (CONFG instead of proper CONFIG) fixed.
| >The error was catched by Venkatesh Pallipadi, thanks a lot Venkatesh!
| >See details on http://lkml.org/lkml/2008/10/9/425
| >
| >Reported-by: Venkatesh Pallipad <venkatesh.pallipadi@...el.com>
| >Signed-off-by: Cyrill Gorcunov <gorcunov@...il.com>
| >---
| >
| >Index: linux-2.6.git/arch/x86/kernel/apic.c
| >===================================================================
| >--- linux-2.6.git.orig/arch/x86/kernel/apic.c   2008-09-26
| >20:43:47.000000000 +0400
| >+++ linux-2.6.git/arch/x86/kernel/apic.c        2008-10-10
| >16:37:26.000000000 +0400
| >@@ -332,11 +332,7 @@ int lapic_get_maxlvt(void)
| >  */
| >
| > /* Clock divisor */
| >-#ifdef CONFG_X86_64
| >-#define APIC_DIVISOR 1
| >-#else
| > #define APIC_DIVISOR 16
| >-#endif
| >
| > /*
| >  * This function sets up the local APIC timer, with a timeout of
| >@@ -592,10 +588,10 @@ static int __init calibrate_APIC_clock(v
| >        global_clock_event->event_handler = lapic_cal_handler;
| >
| >        /*
| >-        * Setup the APIC counter to 1e9. There is no way the lapic
| >+        * Setup the APIC counter to maximum. There is no way the lapic
| >         * can underflow in the 100ms detection time frame
| >         */
| >-       __setup_APIC_LVTT(1000000000, 0, 0);
| >+       __setup_APIC_LVTT(0xffffffff, 0, 0);
| >
| >        /* Let the interrupts run */
| >        local_irq_enable();
| >
| 
| Agree with the APIC_DIVISOR part.
| 
| But, not sure why/how the second change is related to this APIC_DIVISOR being 16.
| Also, another nit. Technically we are not setting the "APIC counter to maximum"
| as we do divide by 16 before programming initial count register in __setup_APIC_LVTT().
| 
| Thanks,
| Venki
| 

>From __setup_APIC_LVTT(0xffffffff, 0, 0) caller point of view we do
set maximum possible value. How you could make it bigger?
(without additional changes _inside_ __setup_APIC_LVTT itself).
Actually I wouldn't mind if you fix the comment if you don't like
this 'correlation' btw CLKs divisor and APIC_DIVISOR. No problem :)

		- Cyrill -
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