Fundamental performance constraints in horizontal fusion of in-order cores

A conceptually appealing approach to supporting a broad range of workloads is a system comprising many small cores that can be fused, on demand, into larger cores. We demonstrate that using in-order cores for this purpose, even under idealized assumptions about fusion-related overheads, would introduce fundamental obstacles to achieving good performance -- obstacles that are not present when out-oforder cores are used. Matching the performance of modern dynamically-scheduled designs demands that a fused machine be able to simultaneously manage a large number of active dataflow chains, many more than the amount of ILP typically extracted from the code. When it is in-order cores that are fused, this requirement, in turn, demands either that the active dataflow chains be carefully interleaved among the available issue queues, or that enough cores be provided for them to reside at distinct queues. Using an abstract model for reasoning about the performance of these machines, we show that ...

• Type: Conference
• Year: 2008
• Where: HPCA
• Authors: Pierre Salverda, Craig B. Zilles
• Keywords: Computer Architecture, Constituent Cores, HPCA 2008, In-order Cores, Larger Cores