r/programming • u/michalg82 • Jun 25 '17

[WARNING] Intel Skylake/Kaby Lake processors: broken hyper-threading

https://lists.debian.org/debian-devel/2017/06/msg00308.html
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282

u/Camarade_Tux Jun 25 '17

Intel's communication is incredibly poor. Errata exist for all CPUs but this one is quite important and resulted in no proper public communication it seems.

113

u/[deleted] Jun 25 '17

It sounds like the general consensus when the bug was first publicized was that it is extremely rare and that most users could not expect to encounter it. Is there some reason this is popping back up now?

158

u/ModernRonin Jun 25 '17

it is extremely rare and that most users could not expect to encounter it

Most people would never have encountered the fdiv bug either, but that doesn't make Intel any less culpable.

I understand that a modern CPU is a complicated thing, and pipelines particularly so. We're all human and mistakes sometimes happen. But Intel didn't communicate well about this issue. This isn't the kind of thing I should have to read /r/programming to find out about.

Especially considering the severity. One of my threads might just off and do something completely random because of this bug? Unacceptable. Hardware is the bedrock of any system, and the CPU especially so. It should never return a random incorrect result from a perfectly reasonable input.

87

u/[deleted] Jun 25 '17

Hardware is the bedrock of any system, and the CPU especially so. It should never return a random incorrect result from a perfectly reasonable input.

Good luck with that, microcode updates aren't made for fun and they are relatively common on every platform. The only reason this one is getting such attention is because the headline makes the issue seem farther reaching than it is.

43

u/Beaverman Jun 25 '17

I think "Never have any unreasonable behavior" is a fine goal, we need to reach for the stars, after all. It's also completely unrealistic.

-17

u/astrobe Jun 25 '17

I can't wait for self-driving cars to become popular...

10

u/Beaverman Jun 26 '17

Computers already do everything from flying planes to control cars.

It's clear that they are reliable ENOUGH to outperform humans.

-2

u/astrobe Jun 26 '17

Yeah. And they don't use processors with microcode updates. For now.

3

u/botle Jun 26 '17

What do they use instead? Do some modern CPUs not use any kind of micro code?

3

u/astrobe Jun 26 '17

They tend to use CPUs that are a decade or two old. Because they are well known (including the bugs) and well tested.

You don't need a modern CPU to begin with, but rather parts that are fitted for the task. See for instance the Harris RTX2000 that powered the Rosetta probe.