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Message-ID: <20090118190849.GB858@elte.hu>
Date: Sun, 18 Jan 2009 20:08:49 +0100
From: Ingo Molnar <mingo@...e.hu>
To: Jack Steiner <steiner@....com>
Cc: Mike Travis <travis@....com>, LKML <linux-kernel@...r.kernel.org>,
"H. Peter Anvin" <hpa@...or.com>,
Thomas Gleixner <tglx@...utronix.de>,
Yinghai Lu <yinghai@...nel.org>,
"Maciej W. Rozycki" <macro@...ux-mips.org>
Subject: Re: [PATCH] x86: put trigger in to detect mismatched apic versions.
* Jack Steiner <steiner@....com> wrote:
> > Btw, I checked with our UV architect and the problem is that we need a
> > 16 bit apic id which is what caused the MAX_APICS to be bumped to 32k.
> > The lower 8 bits are the normal apic id, and the upper bit relate to
> > the node. This means cpu 0 on node 0 has the same apic id as cpu 0 on
> > node 1, etc. I also asked about whether we could rely on always
> > having
>
> Not strictly true. The apicids in the ACPI tables are always globally
> unique across the entire system. Because of the size of UV systems, UV
> needs 16 bit apicids. This fits in the ACPI apicid id/eid fields.
>
> The actual processor apicid register is unfortunately only 11 bits and
> there are some restrictions on the actual values loaded into the apicid
> register.
>
> If we can put unique ids into the apicid register, we do. If we can't,
> the function that reads the apicid will automatically supply the rest of
> the bits. Most of the kernel is unaware that the processor apicid
> register may have only a subset of the bits that are in the ACPI tables.
apicid remapping is something we need/want, so we cannot remove that
array. But it would be nice to offload such properties to the percpu area
instead - is there any reason why that is hard? The local apic is attached
to a CPU in any case. Is there some early init reason that complicates
this?
Ingo
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