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Intel Skylake/Kaby Lake processors: broken hyper-threading

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Re: Intel Skylake/Kaby Lake processors: broken hyper-threading

#61

Post by decisiveness »

onli wrote: post #14

Rule of thumb: On a desktop, if you have an i5 you do not have Hyperthreading. All i3s and i7s do have Hyperthreading, as do new Kaby Lake Pentiums (G4560, 4600, 4620). On laptops, some i5s are not real quad cores but dual cores with Hyperthreading.

>Rule of thumb: On a desktop, if you have an i5 you do not have Hyperthreading. All i3s and i7s do have Hyperthreading, as do new Kaby Lake Pentiums (G4560, 4600, 4620).

Hmm...either this statement is wrong or this desktop /proc/cpinfo is wrong:

    $ grep -E 'model|stepping|cpu cores' /proc/cpuinfo | sort -u
    cpu cores	    : 4
    model           : 94
    model name	    : Intel(R) Core(TM) i5-6600 CPU @ 3.30GHz
    stepping	    : 3
    $ grep -q '^flags.*[[:space:]]ht[[:space:]]' /proc/cpuinfo && echo "Hyper-threading is supported"
    Hyper-threading is supported
Intel's product spec page[1] lists this CPU as not supporting Hyper-Threading so I'm a bit puzzled as to why the ht flag is present.

[1]https://ark.intel.com/products/88188/Intel-Core-i5-6600-Proc...

Re: Intel Skylake/Kaby Lake processors: broken hyper-threading

#62

Post by ncrmro »

Just got the 2017 no touchbar 13 macbook pro with the kaby lake i7. Should I be worried, can I even disable HT with mac. And presumably the update will be provided so the whole laptop is still ok?

I've been using the thunderbolt 3 dock with two external monitors and occasionally get a little glitch prolly loose cable I think.

I've downloaded the bitcoin blockchain, done quite a bit of work in pycharm + chrome, multiple projects, flow and webpack in the background and haven't had any sort of crashes tho.

Re: Intel Skylake/Kaby Lake processors: broken hyper-threading

#63

Post by pedrocr »

Here's how to fix it on a Thinkpad on Linux. I've got a T460s and checked with the script[1] that it was indeed affected. The Debian instructions said to update your BIOS before updating the microcode package so I went to the model support page[2] to the BIOS/UEFI section and downloaded the "BIOS Update (Bootable CD)" one. The changelog included microcode updates so it looked promising[3]. To get the ISO onto a usb drive I did the following:

  $ geteltorito n1cur14w.iso > eltorito-bios.iso # provided by the genisoimage package on Ubuntu
  $ sudo dd if=eltorito-bios.iso of=/dev/sdXXX # replace with your usb drive with care to not write over your disk
I then had a bootable USB drive that I ran by rebooting the computer, pressing Enter and then F12 to get to the boot drive selection and selecting the USB. From then it's just following the options it gives you. It's basically pressing 2 to go into the update and then pressing Y and Enter a few times to tell it you really want to do it. After that just let it reboot a few times and the update is done. After booting again the same test script[1] now said I had an affected CPU but new enough microcode.

[1] https://lists.debian.org/debian-user/2017/06/msg01011.html

[2] http://pcsupport.lenovo.com/pt/en/products/laptops-and-netbo...

[3] https://download.lenovo.com/pccbbs/mobiles/n1cur14w.txt

Re: Intel Skylake/Kaby Lake processors: broken hyper-threading

#65

Post by davidmr »

wbl wrote: post #18
userbinator wrote: post #7

The problem description is short and scary: Problem: Under complex micro-architectural conditions, short loops of less than 64 instructions that use AH, BH, CH or DH registers as well as their corresponding wider register (e.g. RAX, EAX or AX for AH) may cause unpredictable system behavior. This can only happen when both logical processors on the same physical processor are active. I wonder how many users have experi…

CPU manufacturers do do huge amounts of testing, and Intel does formal verification of some functional units. The reliability is far better than most software, in part because making a new release costs billions.

In my limited experience, their root cause analyses are really impressive as well with lots of internal attention and resources. I'm not allowed to talk about any Intel issues, but we reported a very strange issue to Nvidia, sent a couple of dozen cards back and six months later got a truly fascinating report back we with hundreds of pages of compute test result tables and electron microscope images and chemistry lab reports. Anything that hints of a manufacturing problem is taken incredibly seriously.

Re: Intel Skylake/Kaby Lake processors: broken hyper-threading

#66

Post by vertex-four »

angry_octet wrote: post #37
jacquesm wrote: post #26

Earlier quoted context omitted.

What makes you think you were?

Couldn't see multiple comments I made in unrelated threads when reading from an incognito tab. Unless comment delay for non logged in viewers is an undocumented feature? Or this is inception level hellban, where some bots and devil curators lurk. What is even real. Btw good to see your Lego contraption article in IEEE Spectrum.

Pages are cached for significant lengths of time for non-logged-in users.

Re: Intel Skylake/Kaby Lake processors: broken hyper-threading

#67

Post by userbinator »

baq wrote: post #57
throwaway2048 wrote: post #52

Earlier quoted context omitted.

There are hardware bugs that are impossible to fix in microcode. What then?

you make workarounds in software, obviously.

...or recall all the hardware and replace it:

https://en.wikipedia.org/wiki/Pentium_FDIV_bug

Re: Intel Skylake/Kaby Lake processors: broken hyper-threading

#68

Post by hedora »

lima wrote: post #15
riledhel wrote: post #2

Does Windows have a patch for this too? Or just disabling HT is the safest option?

It's safe to assume that Windows distributes the microcode fixes as well.

For some reason, Debian says you need bios updates for certain machines, and Debian packaged microcode for others. I wouldn't be surprised if it is the same for Windows.

Re: Intel Skylake/Kaby Lake processors: broken hyper-threading

#69

Post by my123 »

decisiveness wrote: post #61
onli wrote: post #14

Rule of thumb: On a desktop, if you have an i5 you do not have Hyperthreading. All i3s and i7s do have Hyperthreading, as do new Kaby Lake Pentiums (G4560, 4600, 4620). On laptops, some i5s are not real quad cores but dual cores with Hyperthreading.

>Rule of thumb: On a desktop, if you have an i5 you do not have Hyperthreading. All i3s and i7s do have Hyperthreading, as do new Kaby Lake Pentiums (G4560, 4600, 4620). Hmm...either this statement is wrong or this desktop /proc/cpinfo is wrong: $ grep -E 'model|stepping|cpu cores' /proc/cpuinfo | sort -u cpu cores : 4 model : 94 model name : Intel(R) Core(TM) i5-6600 CPU @ 3.30GHz stepping : 3 $ grep -q '^flags.*[[:…

Do you have 8 threads?

Re: Intel Skylake/Kaby Lake processors: broken hyper-threading

#70

Post by AsyncAwait »

blahman2 wrote: post #55
AsyncAwait wrote: post #43

Earlier quoted context omitted.

It's funny, since many of today's software bugs are due to the legacy of C, faults of which can often times be attributed to mimicking the behaviour CPU hardware too closely. EDIT: My wording was poor, but what I meant was that it's not like hardware vendors do not make bugs happen due to deficiencies in their design, which are not only tolerated, but often reflected in software, which runs counter to OP saying that…

Go back to rust-land now :D

It was meant as a response to OP basically saying that hardware vendors make way fewer bugs that the software ones, which is true, but many bugs of software can arguably be attributed to hardware design, so it's not like they're without fault. Rust has nothing to do with it, not sure why even bring it up.
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