Messages in this thread |  | | Date | Tue, 25 Oct 2016 11:29:08 +0200 | From | Borislav Petkov <> | Subject | 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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