Re: [PATCH 2/3] Add multi-node boot support

From: Steffen Persvold
Date: Thu Oct 27 2011 - 06:47:01 EST

On 10/27/2011 09:30, Ingo Molnar wrote:
+ c->phys_proc_id = node;
+ per_cpu(cpu_llc_id, cpu) = node;
+ }

But more importantly, please first explain why the quirk is needed
(the patch only explains what it does but does not explain why it
needs these changes - other NUMA systems are able to boot without
this quirk).

The issue is that since all AMD CPUs gets their initial APIC Id assigned in the power up process on each individual system, when connecting all systems through Numachip we end up with multiple AMD CPUs with the same "phys_proc_id". This in turn lets Linux think they have the same llc_id and we get a oops somewhere in the scheduler code later on (when scheduler is configured to be numa aware).

If it's absolutely needed then add a proper quirk handler instead of
polluting the generic code.

We wanted to reuse as much of the generic AMD code as possible, but it's tricky because most of that code is based around a single HT fabric design, whereas a NumaChip based systems consists of several HT fabrics connected together thus you will have identical NorthBridge IDs (0-7) etc. shared between all systems.

How would you suggest we add a quirk handler for it ?

Steffen Persvold, Chief Architect NumaChip
Numascale AS -
Tel: +47 92 49 25 54 Skype: spersvold
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