On: Intel's Lion Cove Architecture Preview

[magnio]

You mean 4 cores 8 threads give 22% more throughput than 8 cores 8 threads or 4 cores 4 threads?

[rbanffy → magnio]

Remember core to core coordination takes longer than between threads of the same core.

[sapiogram → magnio]

4c/8t gives more throughput than 4c/4t.

[hajile → sapiogram]

There are definitely workloads where turning off SMT improves performance.

SMT is a crutch. If your frontend is advanced enough to take advantage of the majority of your execution ports, SMT adds no value. SMT only adds value when your frontend can't use your execution ports, but at that point, maybe you're better off with two more simple cores anyway.

With Intel having small e-cores, it starts to become cheaper to add a couple e-cores that guarantee improvement than to make the p-core larger.