A Comparative Evaluation of Hardware-Only and Software-Only Directory Protocols in Shared-Memory Mulitprocessors
|Document type:||Journal Articles|
|Article type:||Original article|
|Author(s):||Håkan Grahn, Per Stenström|
|Title:||A Comparative Evaluation of Hardware-Only and Software-Only Directory Protocols in Shared-Memory Mulitprocessors|
|Journal:||Journal of Systems Architecture|
|Organization:||Blekinge Institute of Technology|
|Department:||Department of Software Engineering and Computer Science (Institutionen för programvaruteknik och datavetenskap)
Dept. of Software Engineering and Computer Science S-372 25 Ronneby
+46 455 38 50 00
|Abstract:||The hardware complexity of hardware-only directory protocols in shared-memory multiprocessors has motivated many researchers to emulate directory management by software handlers executed on the compute processors, called software-only directory protocols.
In this paper, we evaluate the performance and design trade-offs between these two approaches in the same architectural simulation framework driven by eight applications from the SPLASH-2 suite. Our evaluation reveals some common case operations that can be supported by simple hardware mechanisms and can make the performance of software-only directory protocols competitive with that of hardware-only protocols. These mechanisms aim at either reducing the software handler latency or hiding it by overlapping it with the message latencies associated with internode memory transactions. Further, we evaluate the effects of cache block sizes between 16 and 256 bytes as well as two different page placement policies. Overall, we find that a software-only directory protocol enhanced with these mechanisms can reach between 63% and 97% of the baseline hardware-only protocol performance at a lower design complexity.