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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

#171

Post by leovonl »

lorenzhs wrote: post #80
aeleos wrote: post #74

Earlier quoted context omitted.

It wouldn't be a big deal if this was just software, but the fact that Intel allowed a PROCESSOR bug to be reported, tested, and fixed without telling anyone that the bug actually exists is honestly horrible. You can't just let CPU bugs under the run since it can throw the stability and reliability of the entire system into question. The people that reported it shouldn't have to dig through Intel microcode updates an…

> Intel allowed a PROCESSOR bug to be reported, tested, and fixed without telling anyone that the bug actually exists That's just not true. Intel published the erratum in April: https://www3.intel.com/content/dam/www/public/us/en/document... - search for SKL150. It was also clearly noted in Debian's intel-microcode changelog on May 15: http://metadata.ftp-master.debian.org/changelogs/non-free/i/... They absolutely sh…

It's an excuse that is commonly given - but easily avoidable if you care enough about the ones that pay your salary by buying processors from your company.

And not only that, but they did much more than the average Joe and essentially pin-pointed the issue for them. So yeah, inexcusable it is.

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

#172

Post by ComputerGuru »

lorenzhs wrote: post #166
ComputerGuru wrote: post #131

Earlier quoted context omitted.

If this "fix" ends up disabling HT, how can I get a refund not just for the CPU but for the $3k laptop I spec'd around it? Without needing to sue?

That's just the workaround until a fix is available for your CPU, if I understood correctly.

No, that's not what I meant. In the past, Intel's microcode updates have simply disabled the broken functionality as an official solution.

http://techreport.com/news/26911/errata-prompts-intel-to-dis...

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

#173

Post by richdougherty »

yborg wrote: post #84
ourcat wrote: post #11

So will this be affecting most Macbook Pros of the past few years? If so, there's a way to disable hyper-threading, but you need Xcode (Instruments). Open Instruments. Go to Preferences. Choose 'CPU'. Uncheck "Hardware Multi-Threading". Rebooting will reset it.

This is kind of like cutting off your leg because of a hangnail. I've been running a Skylake MBP for more than 6 months for compilation workloads and haven't seen a single processor hang. I'm much more annoyed by the completely unpredictable desktop assignment on monitors when hotplugging DisplayPort connections on multiple displays. This one bothers me every day.

> haven't seen a single processor hang

If there was data corruption you might not notice.

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

#174

Post by bsder »

wyager wrote: post #29
wbl wrote: post #18

Earlier quoted context omitted.

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.

This seems like precisely the sort of thing that a competent manufacturer should rule out formally. Formal verification of individual FUs isn't exactly ambitious... I think we're getting to levels of complexity where the process Intel uses, with lots of different QA and testing teams doing their best to look for bugs, just isn't going to cut it. We need formally verified models transformed step-by-verified-step all t…

Formal verification of a decode unit simply will never happen. The complexity is far too high.

Formally verifying something like a multiplier block is difficult but doable if you care. Formally verifying an FPU is probably at about the limit.

If you want formal verification, you would have to simplify a modern microprocessor a lot.

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

#175

Post by jacquesm »

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.

> Btw good to see your Lego contraption article in IEEE Spectrum.

Oh cool, thank you I didn't even realize it had been published. It's already outdated, the latest re-incarnation has double the drop-off bins for twice the sorting speed.

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

#176

Post by scott_s »

jldugger wrote: post #164
ereyes01 wrote: post #144

Earlier quoted context omitted.

A few past lives ago, I used to work on the AIX kernel at IBM. I once spent a few weeks poring through trace data trying to investigate a very mysterious cache-aligned memory corruption induced by a memory stress test. Our trace data was quite comprehensive, and is always turned on due to its very low overhead. It was concerning enough (and took me long enough) that it eventually sucked in the rest of my team to aid…

Did you by chance see the paper a year back or so outlining that memory errors are more likely to occur near page boundaries? The author's premise was that a lot of 'cosmic rays' are just manufacturing flaws.

Can you provide a citation? I'd like to read it.

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

#177

Post by whitebowen »

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

#178

Post by inferiorhuman »

wbl wrote: post #163
justsid wrote: post #99

Earlier quoted context omitted.

Similarly: Kernel bugs! Once upon a time I spend a good week trying to reproduce a rare crash one of our users saw ever so often (just enough to get our attention, but not enough to get a repro case). Stack traces made no sense and just in general the whole crash made no sense the more I looked at it. Turns out it was a bug in XNUs pthread subsystem, a part where I would have never looked if it weren‘t for desperatio…

Emacs would regularly panic the kernel on one OS X version when I opened preview to look at a pdf and had TeX recompile.

The DVD player on OSX with a MacBook (polycarbonate ones) would occasionally cause a kernel panic if you had 4GB of RAM installed.

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

#179

Post by whitebowen »

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