linux-kernel - Re: [PATCH] x86: add apic probe for genapic 64bit v2

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Date:	Tue, 22 Jul 2008 11:05:17 -0700
From:	"Yinghai Lu" <yhlu.kernel@...il.com>
To:	"Suresh Siddha" <suresh.b.siddha@...el.com>
Cc:	"Ingo Molnar" <mingo@...e.hu>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, "Jack Steiner" <steiner@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: add apic probe for genapic 64bit v2

On Tue, Jul 22, 2008 at 10:57 AM, Suresh Siddha
<suresh.b.siddha@...el.com> wrote:
> On Mon, Jul 21, 2008 at 10:08:21PM -0700, Yinghai Lu wrote:
>>
>> Index: linux-2.6/arch/x86/kernel/genapic_64.c
>> ===================================================================
>> --- linux-2.6.orig/arch/x86/kernel/genapic_64.c
>> +++ linux-2.6/arch/x86/kernel/genapic_64.c
>> -                       genapic = &apic_x2apic_cluster;
> ...
>
>> -       } else
>> -#ifdef CONFIG_ACPI
>> -       /*
>> -        * Quirk: some x86_64 machines can only use physical APIC mode
>> -        * regardless of how many processors are present (x86_64 ES7000
>> -        * is an example).
>> -        */
>> -       if (acpi_gbl_FADT.header.revision > FADT2_REVISION_ID &&
>> -                       (acpi_gbl_FADT.flags & ACPI_FADT_APIC_PHYSICAL))
>> -               genapic = &apic_physflat;
>> -       else
>> -#endif
>> -
>> -       if (max_physical_apicid < 8)
>> -               genapic = &apic_flat;
>> -       else
>> -               genapic = &apic_physflat;
>> -
>> -       printk(KERN_INFO "Setting APIC routing to %s\n", genapic->name);
>> +       if (genapic == &apic_flat) {
>> +               if (max_physical_apicid >= 8)
>
> Yinghai, though not directly realted to this probe cleanup, what is this
> 'max_physical_apicid' doing.
>
> I don't understand the need for this commit.
>
>> commit e0da33646826b66ef933d47ea2fb7a693fd849bf
>> Author: Yinghai Lu <yhlu.kernel@...il.com>
>> Date:   Sun Jun 8 18:29:22 2008 -0700
>>
>>     x86: introduce max_physical_apicid for bigsmp switching
>>
>>     a multi-socket test-system with 3 or 4 ioapics, when 4 dualcore cpus or
>>     2 quadcore cpus installed, needs to switch to bigsmp or physflat.
>>
>>     CPU apic id is [4,11] instead of [0,7], and we need to check max apic
>>     id instead of cpu numbers.
>
> for logical flat, it really shouldn't matter how large the physical apic id
> is. In logical flat, OS programs the LDR and the limitation is the
> number of cpu's which is '8'.

before i clean up 32bit, 64bit already used max_physical_apicid to
check if need to switch to physflat.

for 32bit, if not switch to bigsmp, cpu with physical apic id >=8 can
not be started by BSP.

YH
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