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    Intel Skylake and Kabylake have broken hyper-threading

    Discussion in 'Dell XPS and Studio XPS' started by cloud023, Jun 25, 2017.

  1. cloud023

    cloud023 Notebook Guru

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    Bug discussion here (link 1) and here (link 2).

    TLDR: There is a bug in Skylake and Kabylake processors that causes systems to have unpredictable system behavior w/ hyper-threading when executing short loops of 64 instructions or less and accessing certain registers. In certain machines this may only be fixable by a bios update.
     
    cloud023, Jun 25, 2017
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  2. pressing

    pressing Notebook Deity

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    The only Skylake & Kaby Lake (15 inch) XPS units with hyper-threading are i7 (6700HQ & 7700HQ).

    The XPS i3 & i5 units do not have hyper-threading.
     
    Last edited: Jul 3, 2017
    pressing, Jun 25, 2017
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  3. GoNz0

    GoNz0 Notebook Virtuoso

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    I will await the BIOS update sometime around 2019 then :)
     
    GoNz0, Jun 25, 2017
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  4. pressing

    pressing Notebook Deity

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    Coming just after the SpeedShift update. . .
     
    pressing, Jun 26, 2017
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  5. 6.|THE|1|BOSS|.9

    6.|THE|1|BOSS|.9 Notebook Evangelist

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    6.|THE|1|BOSS|.9, Jun 29, 2017
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  6. GoNz0

    GoNz0 Notebook Virtuoso

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    It has always been my understanding that once the BIOS hands control to the OS it will update the microcode on a software basis, this was confirmed on my Asus PC as being unnecessary once it had booted, fair enough if it won't boot you will need a new BIOS but we should be fine.
     
    GoNz0, Jun 30, 2017
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  7. mazewing

    mazewing Notebook Enthusiast

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    Let's bet $10 that before that Dell will release new versions of the BIOS without the microcode fix.
     
    mazewing, Jun 30, 2017
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  8. kirkyboy

    kirkyboy Notebook Geek

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    kirkyboy, Jul 3, 2017
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  9. pressing

    pressing Notebook Deity

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    pressing, Jul 3, 2017
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  10. Mr.Bricss

    Mr.Bricss Notebook Enthusiast

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    Mr.Bricss, Jul 4, 2017
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  11. GoNz0

    GoNz0 Notebook Virtuoso

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    GoNz0, Jul 4, 2017
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  12. Mr.Bricss

    Mr.Bricss Notebook Enthusiast

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    >> 3. Updated processor microcode
     
    Mr.Bricss, Jul 4, 2017
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  13. GoNz0

    GoNz0 Notebook Virtuoso

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    I saw that and it mentions no fix, with Dell's track record it may not fix what we expect it to fix, especially as they failed to tell us why it has been updated.
     
    GoNz0, Jul 4, 2017
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  14. custom90gt

    custom90gt Doc Mod Super Moderator

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    Intel released a microcode update to fix the hyperthreading bug. Considering the last microcode update was over a year ago, I think it's safe to assume that dell is fixing the bug.
     
    custom90gt, Jul 4, 2017
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  15. GoNz0

    GoNz0 Notebook Virtuoso

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    This is Dell we're talking about!
     
    GoNz0, Jul 5, 2017
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  16. custom90gt

    custom90gt Doc Mod Super Moderator

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    Yeah but there is no way dell would update the microcode for any other reason, even if it meant it would increase performance by 100000%.
     
    custom90gt, Jul 5, 2017
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  17. hmscott

    hmscott Notebook Nobel Laureate

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    Unless the specific reason / fix is listed in the BIOS update info, you don't know for sure what's in it :)

    Assuming has been wrong more often than right in the past about what's in a BIOS update.

    It's better to ask via a support ticket, give them all the info they need to ask someone internally to verify the "Skylake or Kabylake Hyperthreading fix is included in the microcode update from Intel in the new BIOS $version."
     
    hmscott, Jul 5, 2017
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  18. custom90gt

    custom90gt Doc Mod Super Moderator

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    Hah ok. I know what assuming does, but there is no way dell would have updated the microcode for any other reason. You can ask support all you want, but they don't know anything. If they put the microcode that has been released since April, then it's Intel's latest fix.
     
    custom90gt, Jul 5, 2017
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  19. hmscott

    hmscott Notebook Nobel Laureate

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    Perhaps... I can think of at least one instance where we thought Asus had done just that (years ago now), and asking them verified it was not included.

    The date of a BIOS doesn't mean it was made near that date, it's usually made 30-60 days before the issue date, and then tested in the lab and with select customers before shipping it.

    So the microcode may be from months earlier in actuality, which is what was the case with the Asus BIOS. It was 2 more months before the microcode we wanted was included.

    If you can check the microcode level before / after to know what version of Microcode actually gets installed, that would be enough.

    The other thing is, I haven't seen a specific Kabylake directed fix named by Intel for the HT bug, has anyone else?
     
    hmscott, Jul 5, 2017
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  20. custom90gt

    custom90gt Doc Mod Super Moderator

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    Just checked the version with RWeverything and it's the latest version (5e on kabylake). Intel doesn't have a 100% solution to Kabylake yet, however the latest microcode fixes Kabylake processors with signatures 0x806e9 and 0x906e9.
     
    custom90gt, Jul 5, 2017
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  21. GoNz0

    GoNz0 Notebook Virtuoso

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    Yeah I saw in Aida64 it was 5e but as I hadn't found anything about what revision fixes it I wasn't sure. my CPU comes up as 000906E9h so fingers crossed.

    the registry is showing windows and BIOS are both using 5e so it could well be the fix as it matches microsoft.
     
    GoNz0, Jul 5, 2017
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  22. custom90gt

    custom90gt Doc Mod Super Moderator

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    Yeah, 5E is the newest microcode from intel, it was released in April but not available on the intel website until 20170511.

    I'd be shocked if anyone on NBR actually had an issue with the HT though.
     
    custom90gt, Jul 5, 2017
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  23. GoNz0

    GoNz0 Notebook Virtuoso

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    I know, we have had a couple of weird ones on here with BSOD issues but it wasn't reproducible (and as you say bloody slim chance a NBR member causing it) so I doubt it is related.

    I found my codes in here
    HKEY_LOCAL_MACHINE\HARDWARE\DESCRIPTION\System\CentralProcessor\0
    I found it on this post for those looking. https://superuser.com/a/895447

    Explains why the windows file is a few months old, once windows is updated with it's own one (back in april as you say) you shouldn't be able to trigger it even with an older BIOS.

    It would seem Dell stepped up to the mark for a change :)
     
    GoNz0, Jul 5, 2017
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