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SubjectRe: [discuss] Re: [patch 1/3] x86_64: Node local PDA -- early cpu_to_node
On Fri, Dec 02, 2005 at 02:51:56PM -0800, Ravikiran G Thirumalai wrote:
> On Fri, Dec 02, 2005 at 12:43:49PM +0100, Andi Kleen wrote:
> > > +#ifdef CONFIG_ACPI_NUMA
> > > + /*
> > > + * Setup cpu_to_node using the SRAT lapcis & ACPI MADT table
> > > + * info.
> > > + */
> > > + for (i = 0; i < NR_CPUS; i++)
> > > + cpu_to_node[i] = apicid_to_node[x86_cpu_to_apicid[i]];
> > > +#endif
> >
> > This should be in a separate function in srat.c.
>
> OK,
>
> >
> > And are you sure it will work with k8topology.c. Doesn't look like
> > that to me.
>
> I don't have a K8 box yet :(, so I cannot confirm either ways.
> But I thought newer opterons need to use ACPI_NUMA instead...

k8topology still needs to work - e.g. for LinuxBios and users which use
acpi=off and as a fallback for broken SRAT tables. You can't break it right now.

>
> <Kconfig quote>
> config K8_NUMA
> bool "Old style AMD Opteron NUMA detection"
> depends on NUMA
> default y
> help
> Enable K8 NUMA node topology detection. You should say Y here if
> you have a multi processor AMD K8 system. This uses an old
> method to read the NUMA configurtion directly from the builtin
> Northbridge of Opteron. It is recommended to use X86_64_ACPI_NUMA
> instead, which also takes priority if both are compiled in.
> </quote>
>
> Even if K8 detection is used, cpu_pda will have memory allocated from node0
> which is not different from the current state. So this patch helps Opterons
> and EM64t boxes which use ACPI_NUMA, right? Also the newer opteron boxes
> and em64t NUMA boxes can now get node local memory for static per-cpu areas.

Hmm good point. However i would prefer if there was no performance regression
between the two options. However i guess it can be kept like this now.
Just make sure to comment it well.

-Andi

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