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Re: [PATCH] x86/AMD: Apply erratum 688 on machines without a BIOS fix

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On Mon, Oct 24, 2016 at 11:39:47PM +0300, sonofagun@openmailbox.org wrote:
> It does to me! That cpu family is "broken" both on B0 and C0. I think
> that a CPU at 30% load should not have >31% branch misses. For example
> with 5% CPU usage you can't expect to get 10% branch-misses...

Why not? It all depends on the load type, working set and the access
patterns. There's no strong correlation between the load of a machine
and the amount of branch misses...

> Yes but on C0 I got better results. Maybe the BIOS vendor got similar
> results and did not apply the fix.

Well, there's a C0 stepping which doesn't need the fix because it was
fixed in the silicon.

You can check that by doing:

setpci -s 0x18.4 0x164.l

and looking at bit 2. If it is set, the erratum is fixed.

> They use the same BIOS for all machines B0, C0 and that could be the
> reason for not applying the 688 workaround. I think we are going to
> the wrong place here but I will not try to influence you at all. I
> only apply the fix once per boot and I think that we are not supposed
> to apply, remove and then reapply workarounds on the fly.

No, I don't mean that - I'm talking about *not* applying it by default
and when people start seeing issues like that, they can boot their
machines with something like "enable_e688_workaround" or so and it will
get applied then. I.e., an "opt-in" deal.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.

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Re: [PATCH] x86/AMD: Apply erratum 688 on machines without a BIOS fix sonofagun@openmailbox.org - 2016-10-21 18:20 +0200
  Re: [PATCH] x86/AMD: Apply erratum 688 on machines without a BIOS fix Borislav Petkov <bp@alien8.de> - 2016-10-21 18:50 +0200
    Re: [PATCH] x86/AMD: Apply erratum 688 on machines without a BIOS fix sonofagun@openmailbox.org - 2016-10-22 00:00 +0200
      Re: [PATCH] x86/AMD: Apply erratum 688 on machines without a BIOS fix Borislav Petkov <bp@alien8.de> - 2016-10-22 01:10 +0200
        Re: [PATCH] x86/AMD: Apply erratum 688 on machines without a BIOS fix sonofagun@openmailbox.org - 2016-10-22 13:20 +0200
          Re: [PATCH] x86/AMD: Apply erratum 688 on machines without a BIOS fix Borislav Petkov <bp@alien8.de> - 2016-10-22 17:10 +0200
            Re: [PATCH] x86/AMD: Apply erratum 688 on machines without a BIOS fix sonofagun@openmailbox.org - 2016-10-23 11:40 +0200
              Re: [PATCH] x86/AMD: Apply erratum 688 on machines without a BIOS fix Borislav Petkov <bp@alien8.de> - 2016-10-23 12:00 +0200
                Re: [PATCH] x86/AMD: Apply erratum 688 on machines without a BIOS fix sonofagun@openmailbox.org - 2016-10-23 19:10 +0200
                Re: [PATCH] x86/AMD: Apply erratum 688 on machines without a BIOS fix Borislav Petkov <bp@alien8.de> - 2016-10-23 19:30 +0200
                Re: [PATCH] x86/AMD: Apply erratum 688 on machines without a BIOS fix sonofagun@openmailbox.org - 2016-10-23 23:10 +0200
                Re: [PATCH] x86/AMD: Apply erratum 688 on machines without a BIOS fix Borislav Petkov <bp@alien8.de> - 2016-10-23 23:40 +0200
                Re: [PATCH] x86/AMD: Apply erratum 688 on machines without a BIOS fix Borislav Petkov <bp@alien8.de> - 2016-10-24 14:40 +0200
                Re: [PATCH] x86/AMD: Apply erratum 688 on machines without a BIOS fix sonofagun@openmailbox.org - 2016-10-24 15:20 +0200
                Re: [PATCH] x86/AMD: Apply erratum 688 on machines without a BIOS fix Borislav Petkov <bp@alien8.de> - 2016-10-24 19:20 +0200
                Re: [PATCH] x86/AMD: Apply erratum 688 on machines without a BIOS fix sonofagun@openmailbox.org - 2016-10-24 22:50 +0200
                Re: [PATCH] x86/AMD: Apply erratum 688 on machines without a BIOS fix Borislav Petkov <bp@alien8.de> - 2016-10-25 11:30 +0200
                Re: [PATCH] x86/AMD: Apply erratum 688 on machines without a BIOS fix sonofagun@openmailbox.org - 2016-10-25 15:20 +0200

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