Messages in this thread | | | Date | Wed, 1 Feb 2017 22:44:21 +0100 | From | Borislav Petkov <> | Subject | Re: [RFC PATCH] x86/CPU/AMD: Bring back Compute Unit ID |
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On Wed, Feb 01, 2017 at 09:37:02PM +0000, Ghannam, Yazen wrote: > This hunk won't work for SMT enabled systems. It'll cause all threads under > an LLC to be considered SMT siblings. For example, threads 0 &2 will have > different cpu_core_id, so the first check will fail. But it'll match on the > second check since cu_id will be initialized to 0.
Good catch.
> To get around this we can set cu_id for all TOPOEXT systems, and update > cpu_core_id, etc. for SMT enabled systems. This way we can just change > cpu_core_id to cu_id in match_smt().
Ok, so we want to init ->cu_id to something invalid then. -1, for example and then do:
if (c->cu_id != -1 && o->cu_id != -1 && (c->cu_id == o->cu_id)) ...
Alternatively, we can define an X86_FEATURE_COMPUTE_UNITS or so synthetic bit which we can check.
One thing I don't want to do is reuse ->cu_id on systems which don't have CUs.
> I tested this patch, with the above changes, on a Fam17h SMT enabled > system. I'll test with SMT disabled and also on a fully-loaded Fam15h > system soon.
Thanks!
-- Regards/Gruss, Boris.
Good mailing practices for 400: avoid top-posting and trim the reply.
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