On Mon, Jul 24, 2017 at 04:44:45PM +0200, Borislav Petkov wrote:
> On Mon, Jul 24, 2017 at 09:14:18PM +0700, Suravee Suthikulpanit wrote:
> > Actually, this is not totally accurate. My apology. This patch is
> > mainly fix to incorrect core ID in /proc/cpuinfo.
>
> So you're "fixing" only some numbering thing. Because core_id doesn't
> have any influence on anything. Here's on an Intel box I have here:
>
> processor : 0 physical id : 0 core id : 0
> processor : 1 physical id : 1 core id : 0
---8<---
> processor : 62 physical id : 2 core id : 11
> processor : 63 physical id : 3 core id : 11
>
> So those core id numbers can be anything as long as the cpumasks used by
> the scheduler are correct.
And as long as the user is able to find consistent topology
information. (Ie. via /proc/cpuinfo and/or
/sys/bus/cpu/devices/cpuX/topology/)
> > This is due to the cpu_core_id fixup in amd_get_topology() below:
> >
> > /* fixup multi-node processor information */
> > if (nodes_per_socket > 1) {
> > u32 cus_per_node;
> >
> > set_cpu_cap(c, X86_FEATURE_AMD_DCM);
> > cus_per_node = c->x86_max_cores / nodes_per_socket;
> >
> > /* core id has to be in the [0 .. cores_per_node - 1] range
> > */
> > c->cpu_core_id %= cus_per_node;
> > }
>
> AFAICT, Andreas did this for MC at the time:
>
> 4a376ec3a259 ("x86: Fix CPU llc_shared_map information for AMD Magny-Cours")
>
> but I don't think we need to care about core_ids fitting into the node
> range anymore. For the above reason - topology doesn't use core ids.
IIRC this was the way to fix llc_shared_map as CPUID functions could
not be used to figure which cores belong to the same compute unit.
> So you can just as well let ->cpu_core_id be derived from the
> ->initial_apicid as it is being done now in amd_detect_cmp().
>
> In order not to cause any more confusion, you can limit the above fixup
> to anything below F17h so that we don't upset existing users and add a
> big fat comment as to why we're doing this. But if it is only a silly
> numbering thing, I don't see the need for doing that jumping through
> hoops.
>
> --
> Regards/Gruss,
> Boris.
Regards,
Andreas
