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AMD fanboy checking in :)

One of the good OCaml folks over at Jane Street just recently found a bug that crashes systems with Hyperthreading enabled on both Intel Skylake and Kaby Lake as well – just saying:

https://news.ycombinator.com/item?id=14630183

Those hardware bugs are all very disheartening from software folks perspective, doesn't matter which company it pertains... "microcode update" rollseyes

Edit: dear AMD haters, keep the downvotes coming B-) it has only been since May that the first fixes have been rolled out for Skylake / Kaby Lake – and yes, naturally AMD should "fix" (rollseyesagain) their respective issues ASAP but just saying...

https://arstechnica.com/information-technology/2017/06/skyla...

2 comments

I bought my Ryzen CPU already, and going to build a new computer shortly. So I'm literally waiting for that fix.

If you are a Linux user it's fine (had two months on a 1700 with Fedora and zero issues) unless you hit the particular edge case.

Sounds like heavy parallel compiling hits it pretty often. Or you mean even that doesn't happen with every chip? Is it some kind of random hardware defect that's not always present?

I hammer the work machine but not at parallel GCC compiles so whatever the underlying cause it's simply not something I've hit.

Disable hyperthreading, it's overrated anyways

Is it? I know there are workloads when it actually can hurt performance, but are they more common than ones when it helps?

> I know there are workloads when it actually can hurt performance, but are they more common than ones when it helps?

Hyperthreading makes better use of execution units but causes twice as many threads to share memory bandwidth and caches. It's often a good trade-off.

But it's also less valuable for high core-count processors, because workloads that aren't highly parallel will have idle real cores to run other threads on, and highly parallel workloads are more likely to be bottlenecked by memory and caches when there are more cores.

The real question is whether it's faster for your workload. And your hardware. The answer could be different on a system with 8 cores and 2 memory channels than a system with 4 cores and 4 memory channels.

Turn it on and then off and see which is faster for you.

Here's Anandtech's recent SPEC benchmark deltas on hypertheading.

http://www.anandtech.com/show/11544/intel-skylake-ep-vs-amd-...

I see performance increases in every row there, so it must be beneficial in most cases.

comparing single threaded performance vs. two-threads-on-one-core will do that. here's a bunch of real-world tests (mostly gaming) showing HT hurting performance: https://www.techpowerup.com/forums/threads/gaming-benchmarks...

> I know there are workloads when it actually can hurt performance

From what I've seen, performance is only hurt in contrived benchmarks intended to cause slowdowns when HT is in use.

It's not net helpful if it triggers a CPU bug.

Sure, but if it's a feature that's increasing performance without a bug, it's something that should be fixed, otherwise you are paying for broken hardware.

That sucks indeed :(

I just wanted to say that many recent CPUs seem to be rushed efforts - be it Intel or AMD.

They’re not rushed, you just cannot knock out every bug in a new piece of software or hardware in one go. It is not possible (without some incredibly slow and 3xpensove processes).

AMD has pulled up to match or beat Intel, so both companies were absolutely rushing things out. It will settle down and these bugs will get fixed by microcode updates.

Compare what you can get today: an Intel CPU without a hyperthreading problem (fixed in a microcode update months back) or an AMD CPU with a hyperthreading problem (being investigated by AMD for 3 months).

Edit: thanks, s/unacknowledged/being investigated/

If I remember the story right it took Intel ~8months to accept that it was an issue and fix it.

Would you buy a pile of Ryzen CPUs under the assumption that AMD will be able to fix it properly with an update (without e.g. disabling HT or making performance worse as they did for their TLB fix in 2007)? If they take another 2 months, you're out on your return window.

to be fair, that Intel hyperthreading issue took Intel 5 months to investigate and fix.

That bug was acknowledged a while ago.