To: "Tommy Faasen" <tommy@vuurwerk.nl>
cc: linux-kernel@vger.kernel.org
Subject: Re: SMP processor rework help needed
In-Reply-To: <000b01c154ee$1d6a2610$6400a8c0@it0>
From: Andi Kleen <ak@muc.de>
Date: 14 Oct 2001 22:33:27 +0200
In-Reply-To: "Tommy Faasen"'s message of "Sun, 14 Oct 2001 22:23:37 +0200"
Message-ID: <k2wv1yhsh4.fsf@zero.aec.at>
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In article <000b01c154ee$1d6a2610$6400a8c0@it0>,
"Tommy Faasen" <tommy@vuurwerk.nl> writes:
> Hi,
> I have this unique situation where cpu 1 has less features (like fxsr) then
> cpu 0.

I used to have such an AMP machine too: a dual PII-300 with one Katmai and one
Deschutes. It's technically a violation of the specs; the Intel SMP spec
requires that the non boot cpus need to have a superset of the features
of the boot CPU. One CPU died, so it is symmetric now.

For most capabilities it should already work in 2.4 after hpa's cpu 
set rewrite, but FXSAVE is unfortunately a bit of a special case because
it is used in the scheduler context switch and that is required early
in the initialization for SMP bootup and changing it would be very
intrusive.

In the 2.2 SuSE kernel it was fixed instead by adding a new kernel
command line option nofxsave that overrides the FXSAVE bit on the first
CPU. That is ok because such setup is very rare and is only generated by
people who build their own boxes; and these should also know how to pass
kernel command line arguments.

Such an option should also be easy to add to 2.4.
-Andi
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