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Re: [PATCH v3 1/2] x86/AMD: Fix cpu_llc_id for AMD Fam17h systems

From Ingo Molnar <mingo@kernel.org>
Newsgroups linux.kernel
Subject Re: [PATCH v3 1/2] x86/AMD: Fix cpu_llc_id for AMD Fam17h systems
Date 2016-11-07 15:10 +0100
Message-ID <sASMy-4aH-3@gated-at.bofh.it> (permalink)
References <szaaR-2yB-5@gated-at.bofh.it> <szaaR-2yB-3@gated-at.bofh.it> <sAMH7-8iu-21@gated-at.bofh.it> <sAOpA-1ar-33@gated-at.bofh.it>
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* Borislav Petkov <bp@suse.de> wrote:

> On Mon, Nov 07, 2016 at 08:31:21AM +0100, Ingo Molnar wrote:
> > > cpu_llc_id (Last Level Cache ID) derivation on AMD Fam17h has an
> > > underflow bug when extracting the socket_id value. It starts from 0
> 
> How's this...
> 
> > > so subtracting 1 from it will result in an invalid value. This breaks
> > > scheduling topology later on since the cpu_llc_id will be incorrect.
>    ^^^^^^^^^^^^^^^^^^^
> ... here?
> 
> > Same question as for the previous patch: what are the effects of the bug:
> 
> See above.

There's many ways the scheduling topology can 'break', resulting in different 
effects:

 - scheduling domains might be mixed up to the extent of crashing the bootup

 - some cores might be missing altogether, reducing available CPUs in essence

 - cache domains might be seriously mixed up, resulting in serious drop in 
   performance.

 - or domains might be partitioned 'wrong' but not catastrophically 
   wrong, resulting in a minor performance drop (if at all)

... do we know which of these occurs in this situation?

Thanks,

	Ingo

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Re: [PATCH v3 1/2] x86/AMD: Fix cpu_llc_id for AMD Fam17h systems Borislav Petkov <bp@suse.de> - 2016-11-02 21:20 +0100
  Re: [PATCH v3 1/2] x86/AMD: Fix cpu_llc_id for AMD Fam17h systems Ingo Molnar <mingo@kernel.org> - 2016-11-07 08:40 +0100
    Re: [PATCH v3 1/2] x86/AMD: Fix cpu_llc_id for AMD Fam17h systems Borislav Petkov <bp@suse.de> - 2016-11-07 10:30 +0100
      Re: [PATCH v3 1/2] x86/AMD: Fix cpu_llc_id for AMD Fam17h systems Ingo Molnar <mingo@kernel.org> - 2016-11-07 15:10 +0100
        Re: [PATCH v3 1/2] x86/AMD: Fix cpu_llc_id for AMD Fam17h systems Borislav Petkov <bp@suse.de> - 2016-11-07 17:00 +0100
          Re: [PATCH v3 1/2] x86/AMD: Fix cpu_llc_id for AMD Fam17h systems Ingo Molnar <mingo@kernel.org> - 2016-11-08 07:40 +0100
            Re: [PATCH v3 1/2] x86/AMD: Fix cpu_llc_id for AMD Fam17h systems Borislav Petkov <bp@suse.de> - 2016-11-08 09:40 +0100
              Re: [PATCH v3 1/2] x86/AMD: Fix cpu_llc_id for AMD Fam17h systems Ingo Molnar <mingo@kernel.org> - 2016-11-08 11:30 +0100
                Re: [PATCH v3 1/2] x86/AMD: Fix cpu_llc_id for AMD Fam17h systems Borislav Petkov <bp@suse.de> - 2016-11-08 12:10 +0100
                Re: [PATCH v3 1/2] x86/AMD: Fix cpu_llc_id for AMD Fam17h systems Ingo Molnar <mingo@kernel.org> - 2016-11-08 16:00 +0100
                Re: [PATCH v3 1/2] x86/AMD: Fix cpu_llc_id for AMD Fam17h systems Borislav Petkov <bp@suse.de> - 2016-11-08 16:40 +0100
              [tip:x86/urgent] x86/cpu/AMD: Fix cpu_llc_id for AMD Fam17h systems tip-bot for Yazen Ghannam <tipbot@zytor.com> - 2016-11-09 17:20 +0100

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