alt Hacker News>Hyperthreading/SMT is a significant boon for heavily threaded workloads.
That's hugely debatable and depends on SW workloads and the SMT implementation + CPU pipeline design.
In SMT the execution engines, ALUs, FPUs, and caches are completely shared. When one thread stalls waiting for RAM, the second thread sneaks into the idle execution units. At best, SMT yields a ~10% to 20% throughput boost over a single thread.
>Because that description makes the 8 core Bulldozers sound exactly like a 4 core with SMT.
It's not the same thing. Bulldozer arch sits between a true 8-core and 4-core + SMT implementation.
> At best, SMT yields a ~10% to 20% throughput boost over a single thread.
Exactly, which is a significant benefit for how marginal the costs are.
> It's not the same thing. Bulldozer arch sits between a true 8-core and 4-core + SMT implementation.
Then surely it should be even better than 4 cores with SMT?
If you're going to argue that the problem with Bulldozer was it's weird semi-SMT solution, you need to explain how it would've been better without it (aka as a regular quad core). Because even if it just gets the 10-20% performance improvements from being a form of SMT it would be better to have it than to not. And if you have lots of integer unit-bound threads, it should be even better than that.