Publication Data
Probabilistic Distance-based Arbitration: Providing Equality of Service for Many-core CMPs
Abstract: Emerging many-core chip multiprocessors will integrate
dozens of small processing cores with an on-chip interconnect consisting of
point-to-point links. The interconnect enables the processing cores to not onl
communicate, but to share common resources such as main memory resources and I/O
controllers. In this work, we propose an arbitration scheme to enable equality of
service (EoS) in access to a chip's shared resources. That is, we seek to remove any
bias in a core's access to a shared resource based on its location within the CMP. We
propose using probabilistic arbitration combined with distance-based weights to achieve
EoSand overcome the limitation of conventional round-robin arbiter. We describe how
nonlinear weights need to be used with probabilistic arbiters and propose three
different arbitration weight metrics -- fixed weight, constantly increasing weight, and
variably increasing weight. By only modifying the arbitration of an on-chip router, we
do not require any additional buffers or virtual channels and create a simple, low-cost
mechanism for achieving EoS. We evaluate our arbitration scheme across a wide range of
traffic patterns. In addition to providing EoS, the proposed arbitration has additional
benefits which include providing quality-of-service features (such as differentiated
service) and providing fairness in terms of both throughput and latency that approaches
the global fairness achieved with age-base arbitration -- thus, providing a more stable
network by achieving high sustained throughput beyond saturation.
