The twin demands of energy-efficiency and higher performance on
DRAM are highly emphasized in multicore architectures. A variety
of schemes have been proposed to address either the latency or the
energy consumption of DRAMs. These schemes typically require
non-trivial hardware changes and end up improving latency at the
cost of energy or vice-versa.
One specific DRAM performance problem in multicores is that
interleaved accesses from different cores can potentially degrade
row-buffer locality. In this paper, based on the temporal and spatial
locality characteristics of memory accesses, we propose a reorganization
of the existing single large row-buffer in a DRAM
bank into multiple sub-row buffers (MSRB). This re-organization
not only improves row hit rates, and hence the average memory latency,
but also brings down the energy consumed by the DRAM.
The first major contribution of this work is proposing such a reorganization
without requiring any significant changes to the existing
widely accepted DRAM specifications. Our proposed reorganization
improves weighted speedup by 35.8%, 14.5% and 21.6% in
quad, eight and sixteen core workloads along with a 42%, 28% and
31% reduction in DRAM energy.
The proposed MSRB organization enables opportunities for the
management of multiple row-buffers at the memory controller level.
As the memory controller is aware of the behaviour of individual
cores it allows us to implement coordinated buffer allocation
schemes for different cores that take into account program behaviour.
We demonstrate two such schemes, namely Fairness Oriented Allocation
and Performance Oriented Allocation, which show the flexibility
that memory controllers can now exploit in our MSRB organization
to improve overall performance and/or fairness.
Further, the MSRB organization enables additional opportunities
for DRAM intra-bank parallelism and selective early precharging
of the LRU row-buffer to further improve memory access latencies.
These two optimizations together provide an additional 5.9%
performance improvement.