linux-kernel - Re: [patch 00/26] x64, x2apic/intr-remap: Interrupt-remapping and x2apic support

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Date:	Sat, 12 Jul 2008 00:02:54 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	"Yinghai Lu" <yhlu.kernel@...il.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Suresh Siddha" <suresh.b.siddha@...el.com>,
	"Ingo Molnar" <mingo@...e.hu>, "hpa@...or.com" <hpa@...or.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"arjan@...ux.intel.com" <arjan@...ux.intel.com>,
	"andi@...stfloor.org" <andi@...stfloor.org>,
	"jbarnes@...tuousgeek.org" <jbarnes@...tuousgeek.org>,
	"steiner@....com" <steiner@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"jeremy@...p.org" <jeremy@...p.org>
Subject: Re: [patch 00/26] x64, x2apic/intr-remap: Interrupt-remapping and x2apic support

"Yinghai Lu" <yhlu.kernel@...il.com> writes:

> On Fri, Jul 11, 2008 at 8:52 PM, Eric W. Biederman
> <ebiederm@...ssion.com> wrote:
>> "Yinghai Lu" <yhlu.kernel@...il.com> writes:
>>
>>> 1. wonder if x2apic can be use with uniprocessor.
>>>
>>> in APIC_init_uniprocessor, it will try to enable x2apic, but later
>>>
>>> apic_write(APIC_ID, SET_APIC_ID(boot_cpu_physical_apicid));
>>>
>>> but SET_APIC_ID is still for xapic version. so need to GET_APIC_ID,
>>> SET_APIC_ID for different
>>> genapic like 32bit.
>>>
>>> 2 check_x2apic is called in setup_arch, but it only set apic_ops,
>>> and genapic still not changed, aka apic_flat...
>>> wonder if you need to call setup_apic_routing to set genapic.
>>>
>>> otherwise read_apic_id could have use the one from apic_flat....need
>>> to shift......
>>>
>>> 3.or move read_apic_id to apic_ops intead...together with GET_APIC_ID too.
>>> but 32bit version seems like to put GET_APIC_ID with genapic...
>>>
>>> which one is better? 2 or 3
>>
>> Z finish untangle SMP support from apic initialization and move the apic
>> initialization up into init_IRQ.
>>
>> That is better but is likely the wrong short term approach.
>
> plan to add get_apic_id(x) into 64bit genapic, and will use
> #define GET_APIC_ID(x) genapic->get_apic_id(x)
> #define read_apic_id() GET_APIC_ID(apic_read(APIC_ID))
>
> so it is identical to 32bit, and we smooth the merging of 32/64 apic code
>
> also read the x2APIC spec pdf, it doesn't say anything about interrupt
> remapping...need to be used with x2apic...

Clustered logical mode won't work as it requires > 16 bits of apicid.
So only flat physical mode will work.

Eric
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