Probabilistic Distance-based Arbitration: Providing Equality of Service for Many-core CMPs [abstract] (IEEE Xplore, PDF)
Michael M. Lee, John Kim, Dennis Abts, Michael Marty, and Jae W. Lee
Proceedings of the 43rd IEEE/ACM International Symposium on
Microarchitecture (MICRO), December 2010.
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 only 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 in the CMP.
We propose using probabilistic arbitration combined with
distance-based weights to achieve EoS and 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-based arbitration
thus, providing a more stable network by achieving high sustained
throughput beyond saturation.