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SubjectRe: SMP speed on 6x86 UP
On Fri, 20 Mar 1998, MOLNAR Ingo wrote:

> On Fri, 20 Mar 1998, Kurt Garloff wrote:
> > The 6x86 is configured using the processor ports 0x22 and 0x23. Mike Jagdis
> > told me, that the APIC on Intels do use these registers. So, I consider this
> > to be the most probable candidate for the problem.
> yep, if the BIOS lets us so far, this explains things. Could you try
> removing the setup_IO_APIC(); line from smp.c? Does this fix the problem?

A quick look at arch/i386/kernel/smp.c suggests that if an MP
table exists at all we will make some writes to low I/O space
(some would definitely clobber a 6x86 too but I haven't followed
the code paths that closely).

The implication is that motherboard manufacturers are perhaps
standardizing the BIOS' they are shipping and non-SMP boards
are advertising a single CPU MP table.

My quick suggestion would be to change the "if (!smp_found_config)"
test in smp_boot_cpus() to test the processor make as well and
fail anything that isn't Intel.

N.B. It took me longer to write this message than I spent looking
at the code - that's all the time I get for lunch :-).


| Mike Jagdis | Internet: |
| Roan Technology Ltd. | |
| 54A Peach Street, Wokingham | Telephone: +44 118 989 0403 |
| RG40 1XG, ENGLAND | Fax: +44 118 989 1195 |

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