Ajay
Lifer
- Jan 8, 2001
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So, one last time on SMT-4. Here is a simulation based chart based on the Alpha Architecture (doesn't say which alpha was used as a baseline, did in another doc I read in the late 90's but I can't find it). Sadly, the x&y axis are label in light grey. This was clearly a high yield design with what looks like an SMT-2 yield of 67% for integer workloads! FP workloads aren't nearly so impressive, but mixed loading is still good. The rapid falloff with increase hardware thread count is one item that argues against going above SMT-2. In a low yield processor like Zen2 (~30% yield), the technical benefits of moving from SMT-2 to SMT-4 diminish beyond merit (given duplication, and enlargement of cpu resources required to get these marginal gains). Better, for now, to take advantage of shrinks, 3D stacking and other features to increase core count for maximum per socket performance.
Link to paper (1999)
Link to paper (1999)