Re: [RFC PATCH v3 09/13] x86/cpu/topology: Initialize sbm topology after topology parsing

[K Prateek Nayak]

Hello Chenyu,

On 10/3/2026 1:57 PM, Chen Yu wrote:
> Hello Prateek,
> 
> On Thu, Oct 01, 2026 at 07:28:45PM +0000, K Prateek Nayak wrote:
> 
> [ snip ]
> 
>> +static __init void init_sbm_topology(u32 max_apicid)
>> +{
>> +	u32 sbm_shift = x86_topo_system.dom_shifts[TOPO_DIE_DOMAIN] - 1;
> 
> As sashiko reported, and also mentioned here:
> https://lore.kernel.org/lkml/20260510155920.2587431-2-yu.c.chen@xxxxxxxxx/
> Maybe x86_topo_system.dom_shifts[TOPO_DIE_DOMAIN - 1] ?

Ack!

I was testing this on a 2CCX (TILE) = 1 CCD (DIE) machine and I
failed to notice my mistake since:

  x86_topo_system.dom_shifts[TOPO_DIE_DOMAIN] - 1

and

  x86_topo_system.dom_shifts[TOPO_DIE_DOMAIN] - 1

were the same.

> 
>> +	int num_sbm_instances, max_threads_per_instance;
>> +
>> +	/*
>> +	 * On Intel systems, memory controllers are present at TOPO_DIE_DOMAIN.
>> +	 * On newer AMD and Hygon systems, LLC is at TOPO_TILE_DOMAIN so use
>> +	 * that instead.
>> +	 */
>> +	if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD ||
>> +	    boot_cpu_data.x86_vendor == X86_VENDOR_HYGON)
>> +		sbm_shift = x86_topo_system.dom_shifts[TOPO_TILE_DOMAIN] - 1;
> 
> Ditto.

Thank you! Will make sure I pull a VM with weird topology next time
during my testing to see if everything is correct.

-- 
Thanks and Regards,
Prateek