Date: Sat, 22 Feb 2003 01:38:49 +0100 (MET)
From: Mikael Pettersson <mikpe@user.it.uu.se>
Message-Id: <200302220038.h1M0cn6r004153@harpo.it.uu.se>
To: ionut@badula.org, m.c.p@wolk-project.de
Subject: Re: UP local APIC is deadly on SMP Athlon
Cc: jgarzik@pobox.com, linux-kernel@vger.kernel.org
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1437
Lines: 35

On Fri, 21 Feb 2003 22:41:23 +0100, Marc-Christian Petersen wrote:
>> And this is what I found: eliminating two lines from
>> APIC_init_uniprocessor() makes the problem go away.
>> diff -urNX diff_kernel_excludes linux-2.4.10-pre12/arch/i386/kernel/apic.c
>> linux-2.4.10-pre11++/arch/i386/kernel/apic.c ---
>> linux-2.4.10-pre12/arch/i386/kernel/apic.c	Wed Feb 19 23:53:15 2003 +++
>> linux-2.4.10-pre11++/arch/i386/kernel/apic.c	Fri Feb 21 15:37:06 2003 @@
>> -1087,9 +1087,6 @@
>>
>>  	connect_bsp_APIC();
>>
>> -	phys_cpu_present_map = 1;
>> -	apic_write_around(APIC_ID, boot_cpu_id);
>> -
>>  	apic_pm_init2();
>>
>>  	setup_local_APIC();
>>
>> [patch against 2.4.10-pre12, but 2.4.21-pre4 is reasonably similar]
>Don't do this. I am pretty sure it will break all Intels. I still cannot 
>understand why this fixes your AMD Athlon problem.

This is interesting. Very interesting, even. A plain UP_APIC kernel
(with IO_APIC not enabled or not detected) shouldn't need to touch
APIC_ID at all. I strongly suspect this is a remnant of apic.c's old
SMP-only history, and that it should be removed for UP_APIC-only.

I need to get some downtime (zzz...) but I'll look into this ASAP.

/Mikael
-
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