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

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Date:	Sat, 12 Jul 2008 01:11:49 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	"Yinghai Lu" <yhlu.kernel@...il.com>
Cc:	"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:

>>> 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.
>
> current read_apic_id in genx2apic_cluster and genx2apic_phys is the same...

There is a fixed defined mapping between logical & physical mappings,
so that may not be an issue.

A logical cluster apicid is encoded with the high 16bits being the
cluster number, and the low 16bits being a bitmap of which core
in the cluster to send the irq to.  It sounded like a single
cluster can not span multiple sockets.

So in practice if you have 2 sockets you have a cluster id of 1.
Which means physical apic ids over 16 and logical apicids over 65536.

Eric
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